Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Pdf shopping experience:

1. Compare - without doubt the biggest advantage that the Pdf offers shoppers today is the ability to compare thousands of Pdf at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Pdf? Wrong! If the Pdf is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Pdf then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Pdf? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Pdf and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Pdf wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Pdf then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Pdf site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Pdf, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Pdf, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.



{{ Infobox file format| name = Portable Document Format (PDF)| icon = | screenshot = | caption = Adobe Acrobat displaying a PDF in Microsoft Windows Vista displaying a PDF in [Mac OS X-->

The Portable Document Format (PDF) is the [file format created by Adobe Systems in 1993 for document exchange. PDF is used for representing two-dimensional documents in a device-independent and display resolution-independent fixed-layout document format. Each PDF file encapsulates a complete description of a 2-D document (and, with Acrobat 3-D, embedded 3-D documents) that includes the text, fonts, images, and 2-D vector graphics that compose the document.

PDF is an open standard, and is now being prepared for submission as an International Organization for Standardization standard.

History When the PDF first came out in the early 1990s, its general adoption was slow. At that time, the PDF-creation tools (Adobe Acrobat) and the viewing and printing software had to be bought. Early versions of PDF had no support for external hyperlinks, reducing its usefulness on the World Wide Web; the additional size of the PDF document compared to plain text meant significantly longer download times over the slower modems common at the time, and rendering the files was slow on less powerful machines. Additionally, there were competing formats such as Envoy (WordPerfect), Common Ground Digital Paper and even Adobe's own PostScript format (.ps); in those early years, the PDF file was mainly popular in desktop publishing workflow.

Adobe soon started free distribution of the Acrobat Reader (now Adobe Reader) program, and continued supporting the original PDF, which eventually became the de facto standard for printable documents.

The PDF file format has changed several times, as new versions of Adobe Acrobat have been released. There have been eight versions of PDF: 1.0 (1993), 1.1 (1994), 1.2 (1996), 1.3 (1999), 1.4 (2001), 1.5 (2003), 1.6 (2005), and 1.7 (2006), corresponding to Acrobat releases 1.0 to 8.0.

See also History of PDF Openness.

Technical Foundations Anyone may create applications that read and write PDF files without having to pay royalties to Adobe Systems; Adobe holds patents to PDF, but licenses them for royalty-free use in developing software complying with its PDF specification.http://partners.adobe.com/public/developer/support/topic_legal_notices.html

The PDF combines three technologies:



PostScript PostScript is a page description language run in an interpreter (computer software) to generate an image, a process requiring many resources. PDF is a file format, not a programming language, i.e. flow control commands such as if and loop are removed, while graphics commands such as lineto remain.

Often, the PostScript-like PDF code is generated from a source PostScript file. The graphics commands that are output by the PostScript code are collected and Lexical analysis; any files, graphics, or fonts to which the document refers also are collected; then, everything is compressed to a single file. Therefore, the entire PostScript world (fonts, layout, measurements) remains intact.

As a document format, PDF has several advantages over PostScript:



Technical Overview File Structure A PDF file consists primarily of objects, of which there are eight types:Adobe Systems, p. 27

Objects may be either direct (embedded in another object) or indirect. Indirect objects are numbered with an object number and a generation number. An index table called the xref table gives the byte offset of each indirect object from the start of the file.Adobe Systems, pp. 39-40 This design allows for efficient random access to the objects in the file, and also allows for small changes to be made without rewriting the entire file (incremental update).

Beginning with PDF version 1.5, indirect objects may also be located in special streams known as object streams. This technique reduces the size of files that have large numbers of small indirect objects and is especially useful for Tagged PDF.

Imaging Model The basic design of how graphics are represented in PDF is very similar to that of PostScript, except for the use of transparency (graphic), which was added in PDF 1.4.

PDF graphics use a device independent Cartesian coordinate system to describe the surface of a page. A PDF page description can use a Matrix (mathematics) to Scale (ratio), rotate, or skew graphical elements. A key concept in PDF is that of the graphics state, which is a collection of graphical parameters that may be changed, saved, and restored by a page description. PDF has (as of version 1.6) 24 graphics state properties, of which some of the most important are:

Vector Graphics Vector graphics in PDF, as in PostScript, are constructed with paths. Paths are usually made from of lines and Bezier curves, but can also be constructed from the outlines of text. Unlike PostScript, PDF does not allow a single path to mix text outlines with lines and curves. Paths can be stroked, filled, or used for Clipping path. Strokes and fills can use any color set in the graphics state, including patterns.

PDF supports several types of patterns. The simplest is the tiling pattern in which a piece of artwork is specified to be drawn repeatedly. This may a colored tiling pattern, with the colors specified in the pattern object, or an uncolored tiling pattern, which defers color specification to the time the pattern is drawn. Beginning with PDF 1.4 there is also a shading pattern which draws continuously varying colors. There are seven types of shading pattern of which the simplest are the radial shade (Type 2) and axial shade (Type 3).

Raster Images Raster images in PDF (called Image XObjects) are represented by dictionaries with an associated stream. The dictionary described properties of the image, and the stream contains the image data. (Less commonly, a raster image may be embedded directly in a page description as an inline image.) Images are typically filtered for compression purposes. Image filters supported in PDF include the general purpose filters and the image-specific filters

Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of external streams or Alternate Images. Standardized subsets of PDF, including PDF/A and PDF/X, prohibit these techniques.

Text Text in PDF is represented by text elements in page content streams. A text element specifies that characters in should be drawn at certain positions. The characters are specified using the encoding of a selected font resource.

Fonts A font object in PDF is a description of a digital typeface. It may either describe the characteristics of a typeface, or it may include an embedded font file. The latter case is called an embedded font while the former is called an unembedded font. The font files that may be embedded are based on widely used standard digital font formats: Type_1_and_Type_3_fonts (and its compressed variant CFF), TrueType, and (beginning with PDF 1.6) OpenType. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators.

Encodings Within text strings characters are shown using character codes (integers) that map to glyphs in the current font using an encoding. There are a number of built-in encodings, including WinAnsi, MacRoman, and a large number of encodings for East Asian languages. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the Windows and Macintosh operating systems, fonts using these encodings work equally well on any platform.) The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex.

For large fonts or fonts with non-standard glyphs, the special encodings Identity-H (for horizontal writing) and Identity-V (for vertical) are used. With such fonts it is necessary to provide a ToUnicode table if semantic information about the characters is to be preserved.

Transparency The original imaging model of PDF was, like PostScript's, opaque: each object drawn on the page completely replaced anything previously marked in the same location. In PDF 1.4 the imaging model was extended to allow transparency. When transparency is used, new objects interact with previously marked objects to produce blending effects. The addition of transparency to PDF was done by means of new extensions that were designed to be ignored in products written to the PDF 1.3 and earlier specifications. As a result, files that use a small amount of transparency might view acceptably in older viewers, but files making extensive use of transparency could view completely wrong in an older viewer without warning.

The transparency extensions are based on the key concepts of transparency groups, blending modes, shape, and alpha. The model is closely aligned with the features of Adobe Illustrator version 9. The blend modes were based on those used by Adobe Photoshop at the time. When the PDF 1.4 specification was published the formulas for calculating blend modes were kept secret by Adobe. They have since been published.PDF Blend Modes Addendum

Interactive Elements PDF files may contain interactive elements such as annotations and form fields.

Logical Structure and Accessibility A PDF may contain structure information to enable better text extraction and accessibility.

Security and Signatures A PDF file may be encrypted for security, or digitally signed for authentication.

Technical Issues Accessibility PDF files can be created specifically to be accessible for disabled people. Current PDF file formats can include tags (XML), text equivalents, captions, audio descriptions, et cetera. Some software, such as Adobe InDesign, can automatically produce tagged PDFs. Leading screen readers, including JAWS (screen reader), Window-Eyes, Hal, and Kurzweil Educational Systems can read tagged PDFs; current versions of the Acrobat and Acrobat Reader programs can also read PDFs aloud. Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments. Problems remain with adding tags to older PDFs and those that are generated from scanned documents. In these cases, accessibility tags and re-flowing are unavailable, and must be created either manually or with Optical character recognition techniques. These processes are inaccessible to some disabled people. PDF/UA, the PDF/Universal Accessibility Committee, an activity of AIIM, is working on a specification for PDF accessibility based on the PDF 1.6 specification.

One of the major problems with PDF accessibility is that PDF documents have three distinct views, which, depending on the document's creation, can be inconsistent with each other. The three views are (i) the physical view, (ii) the tags view, and (iii) the content view. The physical view is displayed and printed (what most people consider a PDF document). The tags view is what screen readers read (useful for people with poor eyesight). The content view is displayed when the document is re-flowed to Acrobat (useful for people with mobility disability). For a PDF document to be accessible, the three views must be consistent with each other.

Security In 2001, PDF format attachments carrying viruses were first discovered. Virus researchers found that the PDF file viruses activated with Adobe Acrobat, but not with Acrobat Reader. As with all file formats, caution is advised. An up-to-date antivirus program is paramount.

Usage restrictions and monitoring PDFs may be encrypted so that a password is needed to view or edit the contents. The PDF Reference defines both 40-bit and 128-bit encryption, both making use of a complex system of RC4 and MD5. The PDF Reference also defines ways in which third parties can define their own encryption systems for use in PDF.

PDF files may also contain embedded digital rights management restrictions that provide further controls that limit copying, editing or printing. The restrictions on copying, editing, or printing depend on the reader software to obey them, so the security they provide is limited. Printable documents especially might be saved instead as bitmaps and subject to optical character recognition.

The PDF Reference has technical details or see for an end-user overview. Like HTML files, PDF files may submit information to a web server. This could be used to track the IP address of the client PC, a process known as phone home.

Through their LiveCycle Policy Server product, Adobe provides a method to set security policies on specific documents. This can include requiring a user to authenticate and limiting the time frame a document can be accessed or amount of time a document can be opened while offline. Once a PDF document is tied to a policy server and a specific policy, that policy can be changed or revoked by the owner. This controls documents that are otherwise "in the wild." Each document open and close event can also be tracked by the policy server. Policy servers can be set up privately or Adobe offers a public service through Adobe Online Services.

Subsets Proper subsets of PDF have been, or are being, standardized under International Organization for Standardization for several constituencies:



A PDF/H variant (PDF for Healthcare) is being developed.{{cite web|title=New Best Practices Guide Addresses Exchange of Healthcare Information|url=http://www.aiim.org/article-pr.asp?ID=32097|date=2006-10-20|accessdate=2007-03-09|author=AIIM--> However, it may consist more in a set of "best practices" than in a specific format or subset.

Mars See also: Page description markup language According to a 7 December 2006 Government Computer News blog, Joab Jackson writes that Adobe is exploring an XML-based next-generation PDF codenamed Mars: http://www.gcn.com/blogs/tech/42740.html

Adobe has published information about the Mars file format at http://www.adobe.com/go/mars and at http://labs.adobe.com/wiki/index.php/Mars.

The format of graphic elements of Mars is sometimes described simply as “Scalable Vector Graphics”, but according to the 0.8.0 draft specification (§7.4, §7.5) the format is actually merely similar to SVG: it contains both additions to and subtractions from SVG, so it is in general neither viewable by nor creatable with standard SVG tools: some things will look noticeably different between SVG viewers and Mars viewers.

Content A PDF file is often a combination of vector graphics, text, and raster graphics. The basic types of content in a PDF are:



In later PDF revisions, a PDF document can also support links (inside document or web page), forms, JavaScript (initially available as plugin for Acrobat 3.0), or any other types of embedded contents that can be handled using plug-ins.

PDF 1.6 supports interactive 3D documents embedded in the PDF.

Two PDF files which look similar on a computer screen may be of very different sizes. For example, a high resolution raster image takes more space than a low resolution one. Typically higher resolution is needed for printing documents than for displaying them on screen. Other things that may increase the size of a file is embedding full fonts, especially for Asiatic scripts, and storing text as graphics.

Base 14 Fonts There are fourteen typefaces that have a special significance to PDF documents: Times Roman (in standard, italic, bold, and bold oblique), Courier (typeface) (in standard, oblique, bold and bold oblique), Helvetica (in standard, oblique, bold and bold oblique), Symbol (typeface) and Zapf Dingbats. These should always be present (actually present or a close substitute) and so need not be embedded in a PDF. PDF viewers must know about the metrics of these fonts. Other fonts may be substituted if they are not embedded in a PDF.

Versions {|class="wikitable"|-! PDF Version !! Year of Publication !! new features !! supported by Adobe Reader version|-| 1.2 || || FlateDecode || Acrobat Reader 3.0|-| 1.3 || 2000 || || Acrobat Reader 4.0|-| 1.4 || 2001 || JBIG2 ] || Adobe Reader 6.0|-| 1.6 || 2004 || || Adobe Reader 7.0|-| 1.7 || 2007 || || Adobe Reader 8.0|}

Implementations Readers for many Platform (computing) are available, such as Adobe Reader, Foxit, Preview (software), Xpdf, Evince, Okular, and KPDF; there are also front-ends for many platforms to Ghostscript. PDF readers are generally free. There are many software options for creating PDFs, including the PDF printing capability built in to Mac OS X, the multi-platform OpenOffice.org, Microsoft Office 2007 (an additional free download from Microsoft is required), Wordperfect since version 9, numerous PDF print drivers for Microsoft Windows, the pdfTeX typesetting system, the DocBook PDF tools and Adobe Acrobat itself. There is also specialized software for editing PDF files.

AGFA introduced and shipped Apogee, the very first prepress workflow system based on PDF in 1997.

PDF was selected as the "native" metafile format for Mac OS X, replacing the PICT format of the earlier Mac OS. The imaging model of the Quartz (graphics layer) graphics layer of Mac OS X is based on the model common to Display PostScript and PDF, leading to the nickname "Display PDF". The Preview application can display PDF files, and the version of Safari (web browser) in Mac OS X v10.4 can display PDF files as well. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the Print command. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was also captured as a PDF; in 10.4 the default behaviour is set to capture as a PNG file, though this behaviour can be set back to PDF if required.

Some printers also support direct PDF printing, which can interpret PDF data without external help. Currently, all PDF capable printers also support PostScript, but most PostScript printers do not support direct PDF printing.

See also

References External links



{{ Infobox file format| name = Portable Document Format (PDF)| icon = | screenshot = | caption = Adobe Acrobat displaying a PDF in Microsoft Windows Vista displaying a PDF in [Mac OS X-->

The Portable Document Format (PDF) is the [file format created by Adobe Systems in 1993 for document exchange. PDF is used for representing two-dimensional documents in a device-independent and display resolution-independent fixed-layout document format. Each PDF file encapsulates a complete description of a 2-D document (and, with Acrobat 3-D, embedded 3-D documents) that includes the text, fonts, images, and 2-D vector graphics that compose the document.

PDF is an open standard, and is now being prepared for submission as an International Organization for Standardization standard.

History When the PDF first came out in the early 1990s, its general adoption was slow. At that time, the PDF-creation tools (Adobe Acrobat) and the viewing and printing software had to be bought. Early versions of PDF had no support for external hyperlinks, reducing its usefulness on the World Wide Web; the additional size of the PDF document compared to plain text meant significantly longer download times over the slower modems common at the time, and rendering the files was slow on less powerful machines. Additionally, there were competing formats such as Envoy (WordPerfect), Common Ground Digital Paper and even Adobe's own PostScript format (.ps); in those early years, the PDF file was mainly popular in desktop publishing workflow.

Adobe soon started free distribution of the Acrobat Reader (now Adobe Reader) program, and continued supporting the original PDF, which eventually became the de facto standard for printable documents.

The PDF file format has changed several times, as new versions of Adobe Acrobat have been released. There have been eight versions of PDF: 1.0 (1993), 1.1 (1994), 1.2 (1996), 1.3 (1999), 1.4 (2001), 1.5 (2003), 1.6 (2005), and 1.7 (2006), corresponding to Acrobat releases 1.0 to 8.0.

See also History of PDF Openness.

Technical Foundations Anyone may create applications that read and write PDF files without having to pay royalties to Adobe Systems; Adobe holds patents to PDF, but licenses them for royalty-free use in developing software complying with its PDF specification.http://partners.adobe.com/public/developer/support/topic_legal_notices.html

The PDF combines three technologies:



PostScript PostScript is a page description language run in an interpreter (computer software) to generate an image, a process requiring many resources. PDF is a file format, not a programming language, i.e. flow control commands such as if and loop are removed, while graphics commands such as lineto remain.

Often, the PostScript-like PDF code is generated from a source PostScript file. The graphics commands that are output by the PostScript code are collected and Lexical analysis; any files, graphics, or fonts to which the document refers also are collected; then, everything is compressed to a single file. Therefore, the entire PostScript world (fonts, layout, measurements) remains intact.

As a document format, PDF has several advantages over PostScript:



Technical Overview File Structure A PDF file consists primarily of objects, of which there are eight types:Adobe Systems, p. 27

Objects may be either direct (embedded in another object) or indirect. Indirect objects are numbered with an object number and a generation number. An index table called the xref table gives the byte offset of each indirect object from the start of the file.Adobe Systems, pp. 39-40 This design allows for efficient random access to the objects in the file, and also allows for small changes to be made without rewriting the entire file (incremental update).

Beginning with PDF version 1.5, indirect objects may also be located in special streams known as object streams. This technique reduces the size of files that have large numbers of small indirect objects and is especially useful for Tagged PDF.

Imaging Model The basic design of how graphics are represented in PDF is very similar to that of PostScript, except for the use of transparency (graphic), which was added in PDF 1.4.

PDF graphics use a device independent Cartesian coordinate system to describe the surface of a page. A PDF page description can use a Matrix (mathematics) to Scale (ratio), rotate, or skew graphical elements. A key concept in PDF is that of the graphics state, which is a collection of graphical parameters that may be changed, saved, and restored by a page description. PDF has (as of version 1.6) 24 graphics state properties, of which some of the most important are:

Vector Graphics Vector graphics in PDF, as in PostScript, are constructed with paths. Paths are usually made from of lines and Bezier curves, but can also be constructed from the outlines of text. Unlike PostScript, PDF does not allow a single path to mix text outlines with lines and curves. Paths can be stroked, filled, or used for Clipping path. Strokes and fills can use any color set in the graphics state, including patterns.

PDF supports several types of patterns. The simplest is the tiling pattern in which a piece of artwork is specified to be drawn repeatedly. This may a colored tiling pattern, with the colors specified in the pattern object, or an uncolored tiling pattern, which defers color specification to the time the pattern is drawn. Beginning with PDF 1.4 there is also a shading pattern which draws continuously varying colors. There are seven types of shading pattern of which the simplest are the radial shade (Type 2) and axial shade (Type 3).

Raster Images Raster images in PDF (called Image XObjects) are represented by dictionaries with an associated stream. The dictionary described properties of the image, and the stream contains the image data. (Less commonly, a raster image may be embedded directly in a page description as an inline image.) Images are typically filtered for compression purposes. Image filters supported in PDF include the general purpose filters and the image-specific filters

Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of external streams or Alternate Images. Standardized subsets of PDF, including PDF/A and PDF/X, prohibit these techniques.

Text Text in PDF is represented by text elements in page content streams. A text element specifies that characters in should be drawn at certain positions. The characters are specified using the encoding of a selected font resource.

Fonts A font object in PDF is a description of a digital typeface. It may either describe the characteristics of a typeface, or it may include an embedded font file. The latter case is called an embedded font while the former is called an unembedded font. The font files that may be embedded are based on widely used standard digital font formats: Type_1_and_Type_3_fonts (and its compressed variant CFF), TrueType, and (beginning with PDF 1.6) OpenType. Additionally PDF supports the Type 3 variant in which the components of the font are described by PDF graphic operators.

Encodings Within text strings characters are shown using character codes (integers) that map to glyphs in the current font using an encoding. There are a number of built-in encodings, including WinAnsi, MacRoman, and a large number of encodings for East Asian languages. (Although the WinAnsi and MacRoman encodings are derived from the historical properties of the Windows and Macintosh operating systems, fonts using these encodings work equally well on any platform.) The encoding mechanisms in PDF were designed for Type 1 fonts, and the rules for applying them to TrueType fonts are complex.

For large fonts or fonts with non-standard glyphs, the special encodings Identity-H (for horizontal writing) and Identity-V (for vertical) are used. With such fonts it is necessary to provide a ToUnicode table if semantic information about the characters is to be preserved.

Transparency The original imaging model of PDF was, like PostScript's, opaque: each object drawn on the page completely replaced anything previously marked in the same location. In PDF 1.4 the imaging model was extended to allow transparency. When transparency is used, new objects interact with previously marked objects to produce blending effects. The addition of transparency to PDF was done by means of new extensions that were designed to be ignored in products written to the PDF 1.3 and earlier specifications. As a result, files that use a small amount of transparency might view acceptably in older viewers, but files making extensive use of transparency could view completely wrong in an older viewer without warning.

The transparency extensions are based on the key concepts of transparency groups, blending modes, shape, and alpha. The model is closely aligned with the features of Adobe Illustrator version 9. The blend modes were based on those used by Adobe Photoshop at the time. When the PDF 1.4 specification was published the formulas for calculating blend modes were kept secret by Adobe. They have since been published.PDF Blend Modes Addendum

Interactive Elements PDF files may contain interactive elements such as annotations and form fields.

Logical Structure and Accessibility A PDF may contain structure information to enable better text extraction and accessibility.

Security and Signatures A PDF file may be encrypted for security, or digitally signed for authentication.

Technical Issues Accessibility PDF files can be created specifically to be accessible for disabled people. Current PDF file formats can include tags (XML), text equivalents, captions, audio descriptions, et cetera. Some software, such as Adobe InDesign, can automatically produce tagged PDFs. Leading screen readers, including JAWS (screen reader), Window-Eyes, Hal, and Kurzweil Educational Systems can read tagged PDFs; current versions of the Acrobat and Acrobat Reader programs can also read PDFs aloud. Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments. Problems remain with adding tags to older PDFs and those that are generated from scanned documents. In these cases, accessibility tags and re-flowing are unavailable, and must be created either manually or with Optical character recognition techniques. These processes are inaccessible to some disabled people. PDF/UA, the PDF/Universal Accessibility Committee, an activity of AIIM, is working on a specification for PDF accessibility based on the PDF 1.6 specification.

One of the major problems with PDF accessibility is that PDF documents have three distinct views, which, depending on the document's creation, can be inconsistent with each other. The three views are (i) the physical view, (ii) the tags view, and (iii) the content view. The physical view is displayed and printed (what most people consider a PDF document). The tags view is what screen readers read (useful for people with poor eyesight). The content view is displayed when the document is re-flowed to Acrobat (useful for people with mobility disability). For a PDF document to be accessible, the three views must be consistent with each other.

Security In 2001, PDF format attachments carrying viruses were first discovered. Virus researchers found that the PDF file viruses activated with Adobe Acrobat, but not with Acrobat Reader. As with all file formats, caution is advised. An up-to-date antivirus program is paramount.

Usage restrictions and monitoring PDFs may be encrypted so that a password is needed to view or edit the contents. The PDF Reference defines both 40-bit and 128-bit encryption, both making use of a complex system of RC4 and MD5. The PDF Reference also defines ways in which third parties can define their own encryption systems for use in PDF.

PDF files may also contain embedded digital rights management restrictions that provide further controls that limit copying, editing or printing. The restrictions on copying, editing, or printing depend on the reader software to obey them, so the security they provide is limited. Printable documents especially might be saved instead as bitmaps and subject to optical character recognition.

The PDF Reference has technical details or see for an end-user overview. Like HTML files, PDF files may submit information to a web server. This could be used to track the IP address of the client PC, a process known as phone home.

Through their LiveCycle Policy Server product, Adobe provides a method to set security policies on specific documents. This can include requiring a user to authenticate and limiting the time frame a document can be accessed or amount of time a document can be opened while offline. Once a PDF document is tied to a policy server and a specific policy, that policy can be changed or revoked by the owner. This controls documents that are otherwise "in the wild." Each document open and close event can also be tracked by the policy server. Policy servers can be set up privately or Adobe offers a public service through Adobe Online Services.

Subsets Proper subsets of PDF have been, or are being, standardized under International Organization for Standardization for several constituencies:



A PDF/H variant (PDF for Healthcare) is being developed.{{cite web|title=New Best Practices Guide Addresses Exchange of Healthcare Information|url=http://www.aiim.org/article-pr.asp?ID=32097|date=2006-10-20|accessdate=2007-03-09|author=AIIM--> However, it may consist more in a set of "best practices" than in a specific format or subset.

Mars See also: Page description markup language According to a 7 December 2006 Government Computer News blog, Joab Jackson writes that Adobe is exploring an XML-based next-generation PDF codenamed Mars: http://www.gcn.com/blogs/tech/42740.html

Adobe has published information about the Mars file format at http://www.adobe.com/go/mars and at http://labs.adobe.com/wiki/index.php/Mars.

The format of graphic elements of Mars is sometimes described simply as “Scalable Vector Graphics”, but according to the 0.8.0 draft specification (§7.4, §7.5) the format is actually merely similar to SVG: it contains both additions to and subtractions from SVG, so it is in general neither viewable by nor creatable with standard SVG tools: some things will look noticeably different between SVG viewers and Mars viewers.

Content A PDF file is often a combination of vector graphics, text, and raster graphics. The basic types of content in a PDF are:



In later PDF revisions, a PDF document can also support links (inside document or web page), forms, JavaScript (initially available as plugin for Acrobat 3.0), or any other types of embedded contents that can be handled using plug-ins.

PDF 1.6 supports interactive 3D documents embedded in the PDF.

Two PDF files which look similar on a computer screen may be of very different sizes. For example, a high resolution raster image takes more space than a low resolution one. Typically higher resolution is needed for printing documents than for displaying them on screen. Other things that may increase the size of a file is embedding full fonts, especially for Asiatic scripts, and storing text as graphics.

Base 14 Fonts There are fourteen typefaces that have a special significance to PDF documents: Times Roman (in standard, italic, bold, and bold oblique), Courier (typeface) (in standard, oblique, bold and bold oblique), Helvetica (in standard, oblique, bold and bold oblique), Symbol (typeface) and Zapf Dingbats. These should always be present (actually present or a close substitute) and so need not be embedded in a PDF. PDF viewers must know about the metrics of these fonts. Other fonts may be substituted if they are not embedded in a PDF.

Versions {|class="wikitable"|-! PDF Version !! Year of Publication !! new features !! supported by Adobe Reader version|-| 1.2 || || FlateDecode || Acrobat Reader 3.0|-| 1.3 || 2000 || || Acrobat Reader 4.0|-| 1.4 || 2001 || JBIG2 ] || Adobe Reader 6.0|-| 1.6 || 2004 || || Adobe Reader 7.0|-| 1.7 || 2007 || || Adobe Reader 8.0|}

Implementations Readers for many Platform (computing) are available, such as Adobe Reader, Foxit, Preview (software), Xpdf, Evince, Okular, and KPDF; there are also front-ends for many platforms to Ghostscript. PDF readers are generally free. There are many software options for creating PDFs, including the PDF printing capability built in to Mac OS X, the multi-platform OpenOffice.org, Microsoft Office 2007 (an additional free download from Microsoft is required), Wordperfect since version 9, numerous PDF print drivers for Microsoft Windows, the pdfTeX typesetting system, the DocBook PDF tools and Adobe Acrobat itself. There is also specialized software for editing PDF files.

AGFA introduced and shipped Apogee, the very first prepress workflow system based on PDF in 1997.

PDF was selected as the "native" metafile format for Mac OS X, replacing the PICT format of the earlier Mac OS. The imaging model of the Quartz (graphics layer) graphics layer of Mac OS X is based on the model common to Display PostScript and PDF, leading to the nickname "Display PDF". The Preview application can display PDF files, and the version of Safari (web browser) in Mac OS X v10.4 can display PDF files as well. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the Print command. When taking a screenshot under Mac OS X versions 10.0 through 10.3, the image was also captured as a PDF; in 10.4 the default behaviour is set to capture as a PNG file, though this behaviour can be set back to PDF if required.

Some printers also support direct PDF printing, which can interpret PDF data without external help. Currently, all PDF capable printers also support PostScript, but most PostScript printers do not support direct PDF printing.

See also

References External links



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