history_lover said:
Just because a book isn't DRMed doesn't mean it's not copyrighted material though - would adding a TOC violate the copyright? I would only mess with public domain books, just in case.
I'm not a copyright lawyer, so take this with a grain of salt, but my understanding would be that as long as you do it only for your personal use and do not distribute it to anyone else, it would be okay.
