Originally Posted by slm
This is probably more work than you meant to do, but you can use Calibre to bulk-convert to RTF. Merge the RTF manually but trivially in Word, add trivial table of contents in Word, save and convert the merged RTF back to Calibre.
At that level of work, it's easier for me to merge the PDFs.
While I'm willing to manually merge 20 source documents in Word, I only do so when I've got no other way of getting the content. In this case, since I'm working from Feedbooks, I can have it output in Sony-sized PDFs with my choice of font & point sizes. I have to manually place the covers in, but that's still faster than the copy-paste-format hassles in Word.
But it's good to know that's possible, because I get epubs from a lot of different sites; I may want to deconstruct & reformat them.