PDFs output with the “Document structure tags for accessibility” and “PDF/A compliant” options checked facilitate the production of accessible PDFs, however the resulting PDF does not comply with the newer PDF/UA standard (ISO 14289-1:2014).

We found the following limitations that prevented Word 2019 (on Windows) from achieving PDF/UA compliance.

[Bounding Boxes]
Images that are inserted into Microsoft Word documents are not output with bounding boxes. Each "Figure" structure element should have a bounding box.

[Table Header scope not set]
Table header cells render as TH elements in the PDF structure tree, which is semantically correct. However, they are missing a scope property to indicate the scope of their application as a table header cell. In most tables where the first row is the table header, the correct scope value for table header cells is “Column”. i.e. They act as headers for the columns in the table. Perhaps the scope value can be set based on the First Column/Last Column/Header Row table design options.

[Automatically generated Table of Contents missing alternate descriptions]
Table of contents are routinely generated automatically using Microsoft Word’s capability to use Heading styles as a reference. Table of contents typically include links to headings within the document.
When output as a PDF, the links have been found to be missing descriptions in their Contents property, which would reasonably be expected to contain the name of the link.

[Incorrect/Missing Tab Order property set on pages]
Each page in a PDF contains a tab order property that determines the sequence of tab key navigation. When a page contains annotations such as table of contents or cross-reference, it is a requirement for the page to have its tab order set to Document Structure, which internally is indicated by the value “S”.

[PDF/UA identifier is not added]
The PDF/UA identifier is metadata added to PDFs that comply with the PDF/UA standard. It denotes that the PDF is compliant.
In cases where Microsoft Word outputs PDFs that comply with all other PDF/UA requirements, such as when the document solely consists of headings and paragraphs, the PDF/UA identifier is not added to the PDF, which effectively renders it non-compliant.

Note:
We tested compliance with PDF/UA by using PDF Accessibility Checker 3 (PAC 3) version 3.0.7.0, a free tool developed by the Access for All foundation, who were founded in Switzerland in 2000 to promote the use of technology for people with disabilities.