@marbles - You wanted a GUI way of doing it,
@Terminal Velocity mentioned googling merging 2 pdf files, because there are tons of free, online converters that will allow you to merge two files in your browser.
Maybe not an ideal solution, but it is a solution nonetheless. And as it’s in your browser, it technically counts as a GUI way of doing it.
Personally, I think pdftk is a
great way of natively merging multiple pdf files. I use it a lot. Very quick and very simple. However, it
is a terminal based solution, so I won’t say any more about that.
From a quick bit of DuckDuckGo-fu, There are several GUI programs for merging pdf files in Linux:
PDFArranger,
PDFChain,
PDF Mix Tool,
PDFJumbler.
I know that PDF Arranger is available in the software repos of most distros. So check your package manager. That will probably be your best bet.
Some distros have slightly older versions of it, but the latest version is also available as a flatpak. So again, PDF Arranger might be a good bet.
As for the other three, (PDF Chain, PDF Mix Tool, PDF Jumbler) - I don’t know a lot about them. They may have pre-built packages available, or you may have to build and install them from source. IDK!