No idea what you tried but I use the deDRM plugin in Calibre and it is very easy. If gen lib doesn't have the mobi, epub, or pdf I just buy it on amazon, and strip the drm so i can send it directly to my friends.
If I like the book or the book has valuable illustration done in color I will purchase the physical copy, otherwise backing up my calibre library according to 3-2-1 is easy peasy.