ConTeXt always produces tagged PDFs, but the quality depends on the
input. The default ConTeXt markup generated by pandoc is optimized for
readability and reuse, not tagging. Enable the tagging
format extension to force markup that is optimized for tagging. For
example:
pandoc -t context+tagging doc.md -o doc.pdfA recent context version should be used, as older
versions contained a bug that lead to invalid PDF metadata.