"Accessibility isn't just about disabilities,
it's about varying degrees of ability to access content."
http://csswizardry.com/2010/03/moving-forward-is-holding-us-back/
Adaptable and machine-readable document
The ability to access content is varying - because of cognitive or physical limitations, the use of small screen devices or the usage situation. Therefore content has to be flexible and adaptable in order to fit to all these different perception requirements.
An accessible PDF document can be used with the adaption features of PDF/UA conforming viewers, readers and assistive technologies. It can be read easily by persons with a disability. The range of disabilities include
- various degrees of vision impairment,
- limited motor skills (reduced ability to use traditional controls such as a mouse),
- dyslexia or
- learning difficulties.
A standard PDF document, in contrast, will not be fully accessible to a user of assistive technology nor to many other users with disabilities.
ISO standard defines the requirements
The backbones of an accessible PDF are in short:
- unicode mapping of all characters
- tags that provide informations about the logical document structure (logical order, structure type)
- additional informations such as alternate text descriptions for pictures or charts for example
All the necessary accessiblity features of an accessible PDF document are defined in the ISO standard 14289 (PDF/UA).
Free and quick evaluation tool
In order to get a first clue if your PDF is accessible or not, use the freeware PDF Accessibility Checker (PAC) - it offers an automated PDF/UA-check and gives you an evaluation summary in seconds. Additional it offers a screenreader preview for a quick visual check. If you want to go deeper into the topic, have a look at the detailed evaluation report or the tag tree itself.