The best pdf editor in linux is, IMO, Master PDF. That is not, however, an open source application: to get its full function you must buy a (quite expensive) license.
You can bypass this problem using a previous pdf master release, that have less features, but all free. Remember to lock (pin) this relaese, otherwise your software manager will update it to the new ones.
There are others pdf editor, but not so good
- LibreDraw i.g. can edit a pdf, but the result a very untidy (detroying original formattation) and huge-sized (4 or 5 bigger than the original one) page.
- Scribus can edit a pdf, but not the outlines, and in a very poor mode. Moreover big pdf files are a problem for Scribus.