![Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.](http://web.archive.org./web/20110810114420im_/http://cdn.wn.com/pd/f5/75/2f7316d686678d29be090cccf821_grande.jpg "Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.")
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| Name | Portable Document Format |
|---|---|
| Icon | |
| Iconcaption | Adobe Reader icon |
| Screenshot | |
| Caption | |
| Extension | |
| Typecode | 'PDF ' (including a single space) |
| Uniform type | com.adobe.pdf |
| Magic | %PDF |
| Owner | Adobe Systems |
| Released | |
| Latest release version | 1.7 |
| Latest release date | |
| Standard | ISO 32000-1:2008 |
| Url | Adobe PDF Reference Archives |
In 1991 Adobe Systems co-founder John Warnock outlined a system called "Camelot" that evolved into the Portable Document Format (PDF).
Originally a proprietary format, PDF was officially released as an open standard on July 1, 2008, and published by the International Organization for Standardization as ISO 32000-1:2008. The ISO 32000-1 allows use of some specifications, which are not standardized (e.g. Adobe XML Forms Architecture). ISO 32000-1 does not specify methods for validating the conformance of PDF files or readers. Adobe Acrobat, Adobe's suite for reading and creating PDF files, was not freely available; early versions of PDF had no support for external hyperlinks, reducing its usefulness on the Internet; the larger size of a PDF document compared to plain text required longer download times over the slower modems common at the time; and rendering PDF files was slow on the less powerful machines of the day.
Additionally, there were competing formats such as Envoy, Common Ground Digital Paper, Farallon Replica and even Adobe's own PostScript format (.ps); in those early years, PDF was popular mainly in desktop publishing workflows. In 1995, AT&T; Labs commenced work on another electronic document standard targeted at libraries and archives for preserving their books and documents, DjVu. This standard has evolved into the .djv/ .djvu format, which has had growing success and penetration in the online world for eBooks, catalogs, and image-sharing.
Adobe soon started distributing its Acrobat Reader (now Adobe Reader) program at no cost, and continued supporting the original PDF, which eventually became the de facto standard for printable documents on the web (a standard web document).
The ISO standard ISO 32000-1:2008 is equivalent to Adobe's PDF 1.7. Adobe declared that it is not producing a PDF 1.8 Reference. The future versions of the PDF Specification will be produced by ISO technical committees. However, Adobe published documents specifying what extended features for PDF, beyond ISO 32000-1 (PDF 1.7), are supported in its newly released products. This makes use of the extensibility features of PDF as documented in ISO 32000-1 in Annex E. Adobe declared all extended features in Adobe Extension Level 3 and 5 have been accepted for a new proposal of ISO 32000-2 (a.k.a. PDF 2.0).
The specifications for PDF are backward inclusive. The PDF 1.7 specification includes all of the functionality previously documented in the Adobe PDF Specifications for versions 1.0 through 1.6. Where Adobe removed certain features of PDF from their standard, they too are not contained in ISO 32000-1. || Acrobat Reader 2.0 |- | 1.2 || First edition revised || 1996 || Interactive page elements (such as radio buttons and checkboxes); interactive, fill-in forms (AcroForm); Forms Data Format (FDF) for interactive form data that can be imported, exported, transmitted and received from the Web; mouse events; support for playing movies from external files; support for playing sounds, either embedded in the PDF file or from external files; zlib/deflate compression of text or binary data; Unicode; advanced color features and image proxying || Acrobat Reader 4.0 |- | 1.4 || Third edition || 2001 || JBIG2; transparency; RC4 encryption key lengths greater than 40bits (40-128bits); enhancements to interactive forms and Forms Data Format (FDF), support for XML form submissions, embedded FDF files, Unicode specification of field export values, support for remote collaboration and digital signatures in FDF files; support for accessibility to disabled users; metadata streams using XML - Extensible Metadata Platform (XMP); Tagged PDF ;Facilities for including printer’s marks; Support for the display and preview of production-related page boundaries; New predefined CMaps; Alternate Presentations - alternate ways in which the document may be viewed; The ability to import content from one PDF document into another; EmbeddedFiles entry in the PDF document’s name dictionary - a standard location for the embedded data; OCR text layer || Acrobat Reader 5.0 |- | 1.5 || Fourth edition || 2003 || JPEG 2000; enhanced support for embedding and playback of multimedia; object streams; cross reference streams; XML Forms Data Format (XFDF) for interactive form submission (replaced the XML format in PDF 1.4); support for forms, rich text elements and attributes based on Adobe’s XML Forms Architecture (XFA) 2.02; public-key security handlers using PKCS#7 (introduced in PDF 1.3 but not documented in the PDF Reference until PDF 1.5), public-key encryption, permissions - usage rights (UR) signatures (does not require document encryption), PKCS#7 with SHA-1, RSA up to 4096-bits; security handler can use its own encryption and decryption algorithms; Optional Content - sections of content in a PDF document that can be selectively viewed or hidden by document authors or consumers - for items such as CAD drawings, layered artwork, maps, and multi-language documents; Alternate Presentations - the only type is slideshow - invoked by means of JavaScript actions (Adobe Reader supports only SVG 1.0) Support for Windows 98 dropped. To view and print newer version PDFs, such as those at the IRS website, with older versions of Reader requires downloading in Google Docs "Quick View" simplified PDF format.|| Adobe Reader 6.0 |- | 1.6 || Fifth edition || 2004 || 3D artwork, e.g. support for Universal 3D file format; OpenType font embedding; support for XFA 2.2 rich text elements and attributes; AES encryption; PKCS#7 with SHA256, DSA up to 4096-bits; NChannel color spaces; additional support for embedded file attachments, including cross-document linking to and from embedded files; enhancements and clarifications to digital signatures related to usage rights and modification detection and prevention signatures || || 2011 || Specification not published as of May 2011
There is also the PDF/H, a.k.a. "PDF Healthcare", a Best Practices Guide (BPG), supplemented by an Implementation Guide (IG), published in 2008. PDF Healthcare is not a standard or proposed standard, but only a guide for use with existing standards and other technologies. It is supported by the standards development organizations ASTM and AIIM. PDF/H BPG is based on PDF 1.6.
ISO 32000-1:2008 is the first ISO standard for the full function PDF. The previous ISO PDF standards (PDF/A, PDF/X, etc.) are for more specialized uses. The ISO 32000-1 includes all of the functionality previously documented in the Adobe PDF Specifications for versions 1.0 through 1.6. Adobe removed certain features of PDF from previous versions; these features are not contained in PDF 1.7 either.
ISO 32000-1:2008 specifies a digital form for representing electronic documents to enable users to exchange and view electronic documents independent of the environment in which they were created or the environment in which they are viewed or printed. It is intended for the developer of software that creates PDF files (conforming writers), software that reads existing PDF files and interprets their contents for display and interaction (conforming readers) and PDF products that read and/or write PDF files for a variety of other purposes (conforming products).
The PDF combines three technologies:
![Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.](http://web.archive.org./web/20110810114420im_/http://cdn.wn.com/pd/f5/75/2f7316d686678d29be090cccf821_thumb.jpg "Crewe railway station was completed in 1837 and is one of the most historic railway stations in the world. Built in fields near to Crewe Hall, it originally served the village of Crewe with a population (c. 1831) of just 70 residents.[1] Crewe was chosen after Winsford, seven miles to the north, had rejected an earlier proposal, as had local landowners in neighbouring Nantwich, four miles away.")
if and loop commands. PDF is largely based on PostScript but simplified to remove flow control features like these, 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 tokenized; 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:
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. 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.
There are two layouts to the PDF files—non-linear (not "optimized") and linear ("optimized"). Non-linear PDF files consume less disk space than their linear counterparts, though they are slower to access because portions of the data required to assemble pages of the document are scattered throughout the PDF file. Linear PDF files (also called "optimized" or "web optimized" PDF files) are constructed in a manner that enables them to be read in a Web browser plugin without waiting for the entire file to download, since they are written to disk in a linear (as in page order) fashion. 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.
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.
The concept of a transparency group in PDF specification is independent of existing notions of "group" or "layer" in applications such as Adobe Illustrator. Those groupings reflect logical relationships among objects that are meaningful when editing those objects, but they are not part of the imaging model.
Interactive Forms is a mechanism to add forms to the PDF file format.
PDF currently supports two different methods for integrating data and PDF forms. Both formats today coexist in PDF specification:
Alongside the standard PDF action types, interactive forms (AcroForms) support submitting, resetting, and importing data. The "submit" action transmits the names and values of selected interactive form fields to a specified uniform resource locator (URL). Interactive form field names and values may be submitted in any of the following formats, (depending on the settings of the action’s ExportFormat, SubmitPDF, and XFDF flags): The usage rights (UR) signatures define rights for import form data files in FDF, XFDF and text (CSV/TSV) formats, and export form data files in FDF and XFDF formats. | type code = 'FDF ' | uniform type = | magic = | owner = Adobe Systems | released = (PDF 1.2) | latest release version = | latest release date = | genre = | container for = | contained by = | extended from = PDF | extended to = XFDF | standard = ISO 32000-1:2008 | free = | url = }}
The Forms Data Format (FDF) is based on PDF, it uses the same syntax and has essentially the same file structure, but is much simpler than PDF, since the body of an FDF document consists of only one required object. Forms Data Format is defined in the PDF format specification (since PDF 1.2). The Forms Data Format can be used when submitting form data to a server, receiving the response, and incorporating into the interactive form. It can also be used to export form data to stand-alone files that can be imported back into the corresponding PDF interactive form. Beginning in PDF 1.3, FDF can be used to define a container for annotations that are separate from the PDF document to which they apply. FDF is typically used to encapsulate information such as X.509 certificates, requests for certificates, directory settings, timestamp server settings, and embedded PDF files for network transmission. | type code = 'XFDF' | uniform type = | magic = | owner = Adobe Systems | released = | latest release version = 2.0 | latest release date = | genre = | container for = | contained by = | extended from = PDF, FDF, XML | extended to = | standard = | free = | url = XFDF 2.0 specification }}
XML Forms Data Format (XFDF) is the XML version of Forms Data Format, but the XFDF implements only a subset of FDF containing forms and annotations. There are not XFDF equivalents for some entries in the FDF dictionary - such as the Status, Encoding, JavaScript, Pages keys, EmbeddedFDFs, Differences and Target. The XFDF specification is referenced (but not included) in PDF 1.5 specification (and in later versions). It is described separately in XML Forms Data Format Specification. Adobe XFA Forms are not compatible with AcroForms. Creating XFA Forms for use in Adobe Reader requires Adobe LiveCycle Forms Designer or Avoka SmartForm Composer. Adobe Reader contains "disabled features" for use of XFA Forms, that will activate only when opening a PDF document that was created using enabling technology available only from Adobe. The XFA Forms are not compatible with Adobe Reader prior to version 6.
When the PDF and XFA are combined, the result is a form in which each page of the XFA form overlays a PDF background. This architecture is sometimes referred to as XFAF (XFA Foreground). The alternative is to express all of the form, including boilerplate, directly in XFA. It is sometimes called full XFA.
The standard security provided by Acrobat PDF consists of two different methods and two different passwords, "user password" and "owner password". A PDF document may be protected by password to open ('user' password) and the document may also specify operations that should be restricted even when the document is decrypted: printing, copying text and graphics out of the document, modifying the document, or adding or modifying text notes and AcroForm fields (using 'owner' password). However, all operations (except the document open password protection, if applicable) which are restricted by "owner" or "user" passwords are trivially circumvented by many commonly available "PDF cracking" software and even freely online, and if circumvented these restrictions no longer let the author control what can and cannot be done with the pdf file once distributed. This warning is also displayed when applying such restrictions using Adobe Acrobat software to create or edit PDF files.
Even without removing the password, most freeware or open source PDF readers will ignore the digital rights management "protections" and will allow the user to print or make copy of excerpts of the text as if the document were not limited by password protection.
Later, in PDF 1.4, support was added for the Metadata Streams, using the Extensible Metadata Platform (XMP) to add XML standards-based extensible metadata as used in other file formats. This allows metadata to be attached to any stream in the document, such as information about embedded illustrations, as well as the whole document (attaching to the document catalog), using an extensible schema.
A PDF/H variant (PDF for Healthcare) is being developed. However, it may consist more of a set of "best practices" than of a specific format or subset.
Adobe is exploring an XML-based next-generation PDF code named Mars. Information about the Mars file format is published by Adobe at http://www.adobe.com/go/mars and also http://labs.adobe.com/wiki/index.php/Mars.
The format of graphic elements of Mars is sometimes described simply as "SVG", but according to the version 0.8 draft specification of November 2007 (§3 Mars SVG Support) 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.
The Mars format was effectively dropped in 2008.
One of the significant challenges with PDF accessibility is that Adobe Acrobat is capable of presenting PDF documents in three distinct views, which can be inconsistent with each other for a variety of reasons. Acrobat offers three views: (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 Acrobat's "Reflow" tool is invoked.
There is much confusion on the subject of whether or not Acrobat's "reflow" tool is relevant to accessibility since it does not process the tags tree, and thus cannot correctly represent content that flows between pages. Some feel that the reflow tool is useful for people with mobility disability, and thus take the view that for a PDF document to be accessible, Acrobat's three views must be consistent with each other. In reality, the "content view", and thus Acrobat's Reflow tool (as of Acrobat X) displays the PDF's rendering rather than logical order, and is thus irrelevant to accessibility.
From time to time, new vulnerabilities are discovered in various versions of Adobe Reader, prompting the company to issue security fixes. Other PDF readers are also susceptible. One aggravating factor is that a PDF reader can be configured to start automatically if a web page has an embedded PDF file, providing a vector for attack. If a malicious web page contains an infected PDF file that takes advantage of a vulnerability in the PDF reader, the system may be compromised even if the browser is secure. Some of these vulnerabilities are a result of the PDF standard allowing PDF documents to be scripted with JavaScript. Disabling JavaScript execution in the PDF reader can help mitigate such future exploits, although it will not provide protection against exploits in other parts of the PDF viewing software. Security experts say that JavaScript is not essential for a PDF reader, and that the security benefit that comes from disabling JavaScript outweighs any compatibility issues caused. One way of avoiding PDF file exploits is to have a local or web service convert files to another format before viewing.
On March 30, 2010 security researcher Didier Stevens reported an Adobe Reader and Foxit Reader exploit which runs a malicious executable if the user allows it to launch when asked.
PDF files may also contain embedded DRM 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.
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 phoning home. After update 7.0.5 to Acrobat Reader, the user will be notified "via a dialogue box that the author of the file is auditing usage of the file, and be offered the option of continuing."
Through its 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 timeframe 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. As with other forms of DRM, adherence to these policies and restrictions may or may not be enforced by the reader software being used.
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 - 3D drawings can be embedded using U3D or PRC and various other data formats.
Two PDF files that 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.
There are many software options for creating PDFs, including the PDF printing capabilities built in to Mac OS X and most Linux distributions, the multi-platform OpenOffice.org, Microsoft Office 2007 (if updated to SP2), WordPerfect since version 9, Free PDF XP and numerous PDF print drivers for Microsoft Windows, the pdfTeX typesetting system, the DocBook PDF tools, applications developed around Ghostscript and Adobe Acrobat itself. Google's online office suite Google Docs also allows for uploading, and saving to the Portable Document Format.
Raster image processors (RIPs) are used to convert PDF files into a raster format suitable for imaging onto paper and other media in printers, digital production presses and prepress in a process known as rasterisation. RIPs capable of processing PDF directly include the Adobe PDF Print Engine from Adobe Systems and Jaws and the Harlequin RIP from Global Graphics.
Enfocus PitStop Pro, a plugin for Acrobat, allows manual and automatic editing of PDF files, while the free Enfocus Browser makes it possible to edit the low-level structure of a PDF.
See List of PDF software for a more complete list of PDF editors.
There are also web annotation systems which allow to annotate pdf and other documents formats, e.g. A.nnotate, crocodoc, WebNotes.
In cases where PDFs are expected to have all of the functionality of paper documents, ink annotation is required. Many programs which accept ink input from the mouse are not responsive enough for handwriting using an input tablet or tablet PC. Existing solutions on the PC include Bluebeam PDF Revu, and PDF Annotator.
PDFZilla is an easy-to-use software for PDF conversion. It can convert PDF to Word with all text and graphical data.
A-PDF OCR is a fast desktop utility program that lets you OCR scanned PDF or scanned paper documents into text files or searchable PDF fast and easily.
In 1993 the Jaws RIP from Global Graphics became the first shipping prepress RIP that interpreted PDF natively without conversion to another format. The company released an upgrade to their Harlequin RIP with the same capability in 1997.
Agfa-Gevaert introduced and shipped Apogee, the first prepress workflow system based on PDF, in 1997.
Many commercial offset printers have accepted the submission of press-ready PDF files as a print source, specifically the PDF/X-1a subset and variations of the same. The submission of press-ready PDF files are a replacement for the problematic need for receiving collected native working files.
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 is based on the model common to Display PostScript and PDF, leading to the nickname "Display PDF". The Preview application can display PDF files, as can version 2.0 and later of the Safari web browser. System-level support for PDF allows Mac OS X applications to create PDF documents automatically, provided they support the Print command. The files are then exported in PDF 1.3 format according to the file header. 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 and 10.5 the default behaviour is set to capture as a PNG file, though this behaviour can be set back to PDF if required.
Some desktop 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.
The Free Software Foundation considers one of their high priority projects to be "developing a free, high-quality and fully functional set of libraries and programs that implement the PDF file format and associated technologies to the ISO 32000 standard." The GNUpdf library has, however, not been released yet, while Poppler has enjoyed wider use in applications such as Evince, which comes with the GNOME desktop environment, at the expense of relying on the GPLv2-licensed Xpdf code base that can't be used by GPLv3 programs. There are also commercial development libraries available as listed in List of PDF software.
The Apache PDFBox project of the Apache Software Foundation is an open source Java library for working with PDF documents. PDFBox is licensed under the Apache License.
== See also ==
Category:Article Feedback Pilot Category:Adobe Systems Category:Graphics file formats Category:Electronic documents Category:Open formats Category:Page description languages Category:Vector graphics Category:Computer file formats Category:Digital press Category:ISO standards
This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
