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.

ISO 32000-1:2008 introduced an extension mechanism, to allow vendors or other organizations to establish extensions to the standard without causing difficulties to software. Adobe is using this mechanism to add support for new functionality in its PDF tools. Adobe has indicated that its extensions will cumulate; extensions with higher numbers will incorporate the specifications for extensions with earlier numbers. Thus software that can interpret ExtensionLevel 5 files fully is expected to interpret content compliant with ExtensionLevel 3 too.

ExtensionLevel 3 was published in June 2008, in association with the release of Acrobat 9.0. ExtensionLevel 3 supported substantial additional functionality in the specification. ExtensionLevel 5 was published by Adobe in June 2009, in conjunction with the release of Acrobat 9.1. ExtensionLevel 5 provided very little additional functionality over ExtensionLevel 3; the most significant change is support for a newer version of Adobe's XML Forms Architecture (XFA 3.0)

Adobe Supplement to the ISO 32000, BaseVersion:1.7, ExtensionLevel:3, available at http://www.adobe.com/devnet/acrobat/pdfs/adobe_supplement_iso32000_1.pdf

ISO 32000-1:2008. Document management -- Portable document format -- Part 1: PDF 1.7. An equivalent document is PDF Reference, Sixth Edition, Version 1.7. November 2006. At http://www.adobe.com/devnet/acrobat/pdfs/pdf_reference_1-7.pdf

PDF, Version 1.7, ExtensionLevel 5 provides for very little additional functionality over ExtensionLevel 3. The most significant extension is support for a new version of Adobe's XML Forms Architecture (XFA 3.0).

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. ExtensionLevel 3 was published with the release of Acrobat 9.0 in June 2008. With the release of Acrobat 9.1 in June 2009, Adobe published the specification of ExtensionLevel 5.