Definition
WCAG
The Web Content Accessibility Guidelines — the standard regulations cite (ADA Title II, Section 508, EAA/EN 301 549). For PDFs, WCAG's document-relevant criteria are met by building to PDF/UA practice.
WCAG organizes requirements as perceivable, operable, understandable, robust, at levels A/AA/AAA. Document rules inherit it through EN 301 549 chapter 10 (EU) and the Revised 508 Standards (US), which is why a PDF audit reports WCAG mappings next to PDF/UA checkpoints.
Related tools & guides
Authoritative sources: w3.org
Check whether your PDF is accessible
Ceereo audits any born-digital PDF against PDF/UA and WCAG machine checks for free, then writes the missing accessibility layer into the same file. The document looks exactly the same afterwards.