To elaborate, PDF comparison would be helpful because we can’t use plaintext tools without having to parse and correct poor re-flow due to PDF-isms. That is a lot of work just to make the comparison work properly.
Merging PDFs can cause accessibility issues. I need tools to check them so people with disabilities and/or using assistive tools won’t have a hard time.
uh i think pdf editing like this is a black spot in open source software…
i’m in the happy situation that my pdf are mostly latex generated, so i can even generate diff pdf by using some latex/git scripts.
for merging/simple things i use commandline pdftk and for detailed editing inkscape (does not scale to many pages very well).
diffPDF?
There is an inelegant paid one. I also tried GitHub - vslavik/diff-pdf: A simple tool for visually comparing two PDF files. It does highlight changed parts in the page thumbnails; however, it does this weird overlay in the preview where I can’t read either text.
Two very good pdf viewers are Okular (part of KDE Plasma but you should be able to install it on Xfce) and the Foxit Reader (closed source but there is a free version). Not sure though if you can compare pdfs with them. There is also PDFsam Basic for splitting and merging, but probably you can do that faster in the terminal. I don’t know, maybe not what you are looking for.
I am aware of
and others. Gimp and Inkscape PDF support is comme ci, comme ça.
This would be the best workflow but I am so far removed from latex/git that it would take some time getting used to again. The only issue is that it would only help with PDFs generated by me with latex, so not a swiss army knife by any means.
How are you comparing/editing pdfs on Windows?
Adobe Acrobat Pro obviously. Got it from the City but blocked it from phoning home to continue to use it. Yes, I am a delinquent, which is why I want to reform and find alternatives. 
ATM, it is one app I still appreciate from the Windows / Adobe side. The others I had to use begrudgingly because I have already been using better FLOSS software.
Ah, so it was the right question.
diffpdf is great (not to be confused with diff-pdf)
Thanks for clarifying. Previously, search showed a commercial product. I will give this diffpdf a try. A decent app would save me the trouble of programming something myself.
PS - Never mind, it looks like the same product but I wasn’t aware there was an Ubuntu package.
yeah diffpdf is available for free licensed with GNU GPL, also via ubuntu apt, but only in version 2.1.3. The newer versions are distributed commercially. So far, I have always been happy with 2.1.3 and don’t know what the commercial version would do better.
I noticed an oddity. When scrolling in Firefox, I get a rolling shutter effect. I wonder what that is about. I could make some educated guesses but I would like to know your thoughts too.
Its an X11 thing.
If you don’t mind paying for quality software, try PDF Studio Pro by Qoppa (www dot qoppa dot com) I work in an architectural firm and use advanced features like you mention and more. Yes, it costs a little but it is really, really powerful and well written software.
As in, that is a thing and there is nothing I could do about it, or there is a solution somewhere?
I will take a look but I can’t afford anything nonessential. Welcome to the forum BTW!
Wayland isn’t necessarily any better in this regard. You could be having sync troubles all across the screen. My X11/Firefox is vsynced up.
This is true. While PDF is technically an open format, and largely derived from an earlier open format (PostScript), the specific features that most people closely associate with PDFs are proprietary Adobe features. Even if those features were otherwise mimicked, they wouldn’t work in Adobe’s ubiquitous reader without being signed by Adobe’s key (Adobe Acrobat software).
Years ago, I worked on a tool that did visual diffs of PDFs by rendering them to rasters and comparing pixels. The tool worked on Linux, but unfortunately it was developed as a commercial product so I can’t share it.
Visual comparison is insufficient. I have a method to parse PDF text, used it a few times last year. All I need to do is compare the output.
The upcoming Inkscape 1.2 release supports multi-page PDF editing (import & export). Right now, it’s in beta, but was hinted at being scheduled for release this week. Inkscape 1.2 has a ton of other features too, but multi-page is one of the big ones, along with on-page autoalignment & snapping.
It’s on the Flathub beta remote, which you can add with:
flatpak remote-add --if-not-exists flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo
(And then install Inkscape with flatpak install inkscape and choose the beta version from flathub-beta.)
…or you can just wait a few days. 
For PDF in general, there are a lot of apps that use PDF in some form on Flathub. I’m partial to PDF Arranger for manipulating PDF pages (combining, splitting, rearranging, etc.).
Inkscape 1.2 has been officially released! The blog post has a great overview (nicer and more polished than the release notes on the wiki): What you’ll find inside Inkscape version 1.2 | Inkscape
The release video showcases so many of the huge new features in motion:
(This release is so huge, with so many things I’ve been wanting in Inkscape for decades. It should’ve been called Inkscape 2.0, IMO. Regardless of the version, it’s amazing!)
Also, there’s a pull request to bump up Inkscape to version 1.2 on Flathub, so the update will most likely land today on Flathub (and this will probably be faster than most distros).