A just-published report from the Australian government finds that PDF as a file-format is accessible but that PDF as supported on mobile devices is not.
Noting that mobile devices are a modern reality, including for users with disabilities, the agency states that present-day limitations on mobile devices mean that PDF does not yet qualify as "accessibility supported" per the terms of WCAG 2.0, as is required under Australian law.
To quote the report's summary:
However, the Review also determined that the technical support in the mobile environment was insufficient to claim WCAG 2.0 conformance. Testing of Voiceover (iOS) and Talkback (Android) did not reveal the semantic information from a tagged PDF and bookmark navigation of the document was not available on mobile platforms.
As a result, PDF does not yet have the required accessibility support to fully claim WCAG 2.0 conformance, so it cannot be solely relied upon for the provision of government information except in limited circumstances.
Australian federal government, November 18, 2014