PDF has become a commonplace format for the distribution and exchange of electronic documents. As with other file formats, PDFs need to meet the accessibility requirements that make it possible for people with disabilities to access electronic information.
Acrobat and Accessibility - Adobe
The definitive source from Adobe, this site lists many articles, tutorials, FAQ, tools, and techniques for making content created with Adobe Acrobat more accessible.
This Adobe PDF booklet is a step-by-step guide that covers the basics for creating and optimizing PDF files so that they can be made accessible to users with disabilities such as blindness or low vision.
Making PDF Documents Accessible - Center for Assistive Technology and Environmental Access, Georgia Tech University
Self-paced tutorial covering the Portable Document Format and the various ways it can be made more accessible.
Accessibility and PDF Documents - Web Accessibility Center, Ohio State University
Extensive list of articles, tools, and techniques for making PDF documents more accessible.