In short, Xournal (original, not ++) can add pictures and text too! And it's available via official Debian repository. So it's easier to install in Debian.
Xournal++ is a rewrite of Xournal, and has more features, but I don't want to deal with downloading a .deb or using snap or flatpak. They're working on getting Xournal++ into official Debian repository though, but it's not there yet.
Xournal (original, not ++) is quite good for filling in basic forms on Debian!
It's a very simple but full-featured PDF editor. Makes working with PDF pleasant. I didn't think it would even be possible. Inserting an image is Ctrl+I.