Portable Document Format (PDF) is a file format used to present and exchange documents reliably, independent of software, hardware, or operating system. Invented by Adobe, PDF is now an open standard maintained by the International Organization for Standardization (ISO). PDFs can contain images, links, buttons, form fields, audio, video, and business logic. They can also be signed electronically, commented on and encrypted and are easily viewed using free Acrobat Reader DC software. They are also viewable using Google Drive and other software.
PDF files can be created specifically to be accessible for people with disabilities. PDF file formats in use as of 2014 can include tags (XML), text equivalents, captions, audio descriptions, etc. Tagged PDF is required in the PDF/A-1a specification. Some software can automatically produce tagged PDFs, but this feature is not always enabled by default. Some screen readers, including JAWS, Window-Eyes, Hal, and Kurzweil 1000 and 3000 can read tagged PDFs aloud, as can later versions of the Acrobat and Acrobat Reader programs. Moreover, tagged PDFs can be re-flowed and magnified for readers with visual impairments.
Problems remain with adding tags to older PDFs and those that are generated from scanned documents. In these cases, accessibility tags and re-flowing are unavailable, and must be created either manually or with OCR techniques. These processes are inaccessible to some people with disabilities.