Well I have a PDF document that a colleague sent me, and for whatever reason, the bookmarks are all in one group. That's no problem for me, except that they have random numbers as their names. This is not useful at all when quickly trying to find one of the pages, since it is about 1300 pages long.
Normally, I would go about the painstaking effort of renaming individual pages, but as I just stated, it is 1300 pages long. Now all I need is basically to name them "1", "2", "3", etc. but I have no idea how.