The best programs for editing PDF documents that I have used (and I've tried quite a few) are Adobe Acrobat Pro and Adobe Illustrator. I have not found anything that compares.
But, someone else may have found one. I've tried a lot of different programs, and only had horrible results.
For re-flowing the document, you really need to be able to convert it to an editable format, then edit, then save, then export as a PDF. I have never seen anything that can reasonably convert a PDF to an editable format in a remotely sane manner. Everything I have tried has been complete garbage. And by complete garbage, I mean drive you into a blood thirsty rage level of total chaos that Cthulhu himself couldn't manage. Random crap on a page is a kind description.
I really hope someone can prove me wrong as this problem has plagued me for years.