Originally Posted by Jim Chaffin
I'll simply reopen all those 'chapter' files. Uhmn, where are they?! Nothing but '.epub' files on my drives. Why weren't the originals saved? They are simply text files, pure ASCII, probably.
They are all inside the epub. Unzip the epub (or open it with Sigil) and you'll get your raw files inside. There's nothing arcane about that, an epub file is simply a bunch of text files (not necessarily ASCII, could be utf8 or utf16) zipped with a specific structure.
But Hitch's answer is much more complete, go back and read it if you have been intimidated by its length at first