Sustainability of Digital Formats
 Planning for Library of Congress Collections

PDF (Portable Document Format), developed by Adobe Systems Incorporated, is described by Adobe as a general document representation language. PDF represents formatted, page-oriented documents. These documents may be structured or simple. They may contain text, images, graphics, and other multimedia content, such as video and audio. There is support for annotations, metadata, hypertext links, and bookmarks.

The original version 1.7 of the PDF format was released November 2006 and associated with Acrobat and Adobe Reader 8.0. Version 1.7 was published as ISO 32000-1 in July 2008.

Among other new features, this version of PDF introduces an extensibility mechanism based on an Extensions Dictionary. This mechanism is used by Adobe to introduce new features, but is also available for other vendors or developers to use to establish published extensions. Adobe will maintain a publicly available registry of extensions at http://adobe.com/go/ISO32000Registry. As of September 2010, no extensions beyond those documented by Adobe itself had been registered and the site provided only a registration form.

From the text of ISO 32000-1:2008, "The International Organization for Standardization draws attention to the fact that it is claimed that compliance with this document may involve the use of patents concerning the creation, modification, display and processing of PDF files which are owned by the following parties: Adobe Systems Incorporated, 345 Park Avenue, San Jose, California, 95110-2704, USA. ISO takes no position concerning the evidence, validity and scope of these patent rights. The holders of these patent rights has assured the ISO that they are willing to negotiate licenses under reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this respect, the statements of the holders of these patent rights are registered with ISO. Information may be obtained from those parties listed above."

In association with the adoption of PDF, version 1.7 as an ISO standard (ISO 32000-1:2008), Adobe issued a Public Patent License, granting "every individual and organization in the world the royalty-free right, under all Essential Claims that Adobe owns, to make, have made, use, sell, import and distribute Compliant Implementations."

See PDF for more information from Adobe.

See PDF.

Starting with version 1.7, PDF document files may use extensions developed by organizations other than Adobe. Documents employing these extensions to the baseline specification may not be fully functional in commonly available PDF viewers, such as Adobe Reader. As of September 2010, no extensions have been registered by entities other than Adobe.

ISO 32000-1:2008 introduces an extension mechanism based on an Extensions Dictionary. Extensions will be listed in a registry at http://adobe.com/go/ISO32000Registry. This is one of a small set of functional differences between PDF 1.7 and ISO 32000-1:2008. Some differences probably reflect asynchrony between the Adobe product development cycle and the ISO standardization process.

Both Adobe's PDF Reference for version 1.7 and ISO 32000-1:2008 recommend that "If a PDF file contains binary data, as most do ..., it is recommended that the header line be immediately followed by a comment line containing at least four binary characters—that is, characters whose codes are 128 or greater. This ensures proper behavior of file transfer applications that inspect data near the beginning of a file to determine whether to treat the file’s contents as text or as binary."

PDF 1.7 was released in November 2006 in association with version 8 of Acrobat and Adobe Reader. In January 2007, Adobe announced the intention to pursue standardization through TC 171/SC 2 of ISO. This process led to publication as ISO 32000-1 in July 2008. There are substantial editorial differences between the two specification documents, particularly in the order of material.

To quote from ISO 32000-1:2008, "The first version of PDF was designated PDF 1.0 and was specified by Adobe Systems Incorporated in the PDF Reference 1.0 document published by Adobe and Addison Wesley. Since then, PDF has gone through seven revisions designated as: PDF 1.1, PDF 1.2, PDF 1.3, PDF 1.4, PDF 1.5, PDF 1.6 and PDF 1.7. All non-deprecated features defined in a previous PDF version were also included in the subsequent PDF version. Since ISO 32000-1 is a PDF version matching PDF 1.7, it is also suitable for interpretation of files made to conform with any of the PDF specifications 1.0 through 1.7. Throughout this specification in order to indicate at which point in the sequence of versions a feature was introduced, a notation with a PDF version number in parenthesis (e.g., (PDF 1.3)) is used. Thus if a feature is labelled with (PDF 1.3) it means that PDF 1.0, PDF 1.1 and PDF 1.2 were not specified to support this feature whereas all versions of PDF 1.3 and greater were defined to support it."