The accessibility of an electronic document is dependent on the inclusion of a variety of semantic information such as (but not limited to) machine-recoverable text presented in a declared language, logical structure of content, and organization of that content in pages, sections and paragraphs.
The primary purpose of ISO 14289 (known as PDF/UA) is to define a specific use of the structure and tagged PDF features in PDF 1.7, which provide a mechanism for reuse of PDF page content, especially in the accessibility context.
For PDF/UA conforming files to be truly accessible there must be PDF readers and AT (assistive technology) which understand tagged PDF files. These requirements are also stipulated in the standard.
The original PDF/UA specification published in 2012 is no longer available.
This "dated revision" includes a variety of corrections.
ISO TC 171 SC 2 WG 9 is presently at work on PDF/UA-2.