Portable Document Format (PDF) is a file format developed by Adobe® Systems. PDF makes it possible to send documents with original formatting intact. PDF files are created by scanning an original print document or by using a variety of popular software applications. In order to read PDF files, the user must have Adobe® Acrobat® Reader®, a free application distributed by Adobe Systems.
The growing popularity of PDF has created concerns about accessibility, particularly for users of screen readers. With the release of Adobe® Acrobat® 5.0, Adobe® took significant steps toward improving PDF accessibility. Among other improvements, PDF is now able to communicate more effectively with screen readers, and PDF text can reflow when magnified or when viewed on a handheld computing device.
Adobe's progress is one step toward PDF accessibility, but barriers still exist. Most notably, of the three types of PDF documents—unstructured, structured, and tagged—only tagged PDF files are optimized for accessibility. Few authors are currently creating tagged PDF files, either because this requires additional effort or because of lack of awareness. Authors are also limited by the capabilities of their word processing or desktop publishing tools, many of which have PDF export capabilities that do not currently support tagged PDF format.
PDF security has also created accessibility problems in the past, when PDF documents were encrypted for security purposes in a way that locks out users of assistive technologies, despite the document's being visible on the screen. Newer versions of Acrobat® are better able to separate security from assistive technology access, though it is still possible to select security options that exclude users with disabilities. This unwanted side effect, however, is now clearly documented in security settings dialogs.
Adobe provides accessibility documentation at adobe.com/accessibility . Among other resources available from this site, Adobe has developed a variety of Acrobat accessibility training resources  that describe in detail the process of creating accessible PDF documents using Word, InDesign, and Acrobat Pro.
PDF accessibility also requires that assistive technology (AT) vendors build support into their products and that consumers purchase current upgrades of AT that supports accessible PDF. Two of the most popular screen readers, JAWS® and Window-Eyes™, currently claim to support the new PDF. Freedom Scientific®  has built PDF support into JAWS® 3.7 and higher, and GW Micro  has built PDF support into Window-Eyes 4.1 and higher. Currently, there is no accessibility support for PDF in non-Windows operating systems.
Although it is possible to create an accessible PDF document and possible for a Windows® user to read the document if equipped with the appropriate software, many users and advocacy groups continue to recommend that PDF documents be accompanied by alternative format documents that are more universally accessible, such as HTML.
-  adobe.com/accessibility
-  Acrobat accessibility training resources
-  Freedom Scientific®
-  GW Micro