Ah, this is where things start to get tricky. Or at least where they used to. The world has changed a bit and it turns out that recent versions of LibreOffice Draw do a fantastic job of editing PDF files, and not just adding and deleting pages as you might expect, but for editing text and images as well (so long as your PDF was created directly from a source document and not from a scan). It's not perfect, and I've had it choke up on a few more complex documents, but I'm still impressed with what a good job it does on many of the documents I've had to work with.

Inkscape, too, does a good job with opening documents created elsewhere, and may be a more intuitive choice if your document is heavy on graphics. There are standalone tools as well, like the GPLv2 licensed PDFedit, but I've had such good luck with Inkscape and LibreOffice that I haven't had to use a separate editor in recent years. So there are FOSS PDF editors, and LibreOffice certainly allows you to export to PDF virtually everything

I haven't used any proprietary tools on other systems to compare, but maybe it's satisfactory. It's worked fine for what I've needed to do.