Wasn't PDF supposed to be a read-only, print-only medium? You're supposed to edit the source material (like a doc) and export that to PDF, not edit PDF directly.
Well, there's Acrobat. I think that the issue is that PDF is a deceptively complicated format. It's basically a programming language for describing pages to print. So it's not like parsing a JPG or something, you need a PDF interpreter. And I imagine the Adobe one is encumbered.
Yeah, I use LibreOffice Draw to change out text on PDFs a couple times a month at work. I’ll occasionally get some weird formatting issues or random black lines across the PDF, but usually works well enough, especially if I’m going to be printing the document out.
For something like signing a pdf it was extremely painful to do natively in Linux or with any Foss tools. As of recently Firefox let's you edit, annotate, and sign PDFs. It's honestly one of the biggest steps towards year of the Linux desktop that I've seen in the last 5 years. Linux still has a ways to go but it's getting there slowly.