Slite: yes, I did try the HTML version. It's in some ways worse than the ePub, because even the bitmapped pictures are thrown away. The result is only text, with none of the figures or math preserved. Of course, if your goal is to extract the text and hand-edit it, then this will work.
igorsk: Sure! I'll give PDFConverter a try.
PieOPah: I tried converting Bleak House from the Gutenberg project (fairly plain text). PDFtoEPUB failed with internal Lua errors. I tried extracting a 5 page segment, and even that failed. I now give up.
frabjous: you better believe I've written to them for a refund!