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Background reading on the document standards PolyDoc implements: what they ask for, where the common misreadings are, and which parts a machine can check for you. These are explainers rather than integration steps. For the API side, see the compliance guides.
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WCAG passes, your PDFs still failAccessibility
Why a clean accessibility audit of your website says nothing about the PDFs it links to, and what PDF/UA asks for that WCAG does not.
page.pdf() is not the hard partOperations
What running headless Chrome for PDFs costs once it is a feature rather than a script, and which of the things people buy an API for you can straightforwardly do yourself.