@miki Offline use, inline form filling, and electronic signatures are three distinct classes of problem that should be solved separately. For the case where I buy or otherwise have access to a read-only document that requires none of those, HTML is a fine alternative.

And that was mainly what my post was about: large documents from which I only wish to consume content, but are nevertheless distributed as PDF. It can be perfectly tagged, and pass every manual and automated accessibility check thrown at it. I'll still need to work out why Acrobat is only letting me view one page at a time, and be realistically limited to reading it on a computer.