Hmm… weird about that unsatisfiable font dependency. (did you get any useful info from trying to apt get install the named package?) package appears to be there linky
Not sure how, but I managed to get 3.5.5 installed. Tried to load the docs in question, which worked, then checked version, which was 3.5.4! Killed running libreoffice processes, then tried again, which also worked, and checked version, which was 3.5.5. I suppose I’ll never know what was wrong.