I’ve taken the PDF doc thing a step beyond my first attempt. I converted the single page HTML version of the manual to reStructuredText with Pandoc and then fed that into Sphinx. Sphinx can then go back out to HTML and Tex PDF, etc.
There’s a bunch of stuff that is obviously broken; this is just a proof of concept. Next step would be to take a pass through the reStructuredText to clean it up and maybe think about applying the existing HTML styling. Another idea would be to try to preserve the existing “pagination” in the translation to .rst; for simplicity I just started from the existing single page HTML version.