My system is Debian 12.8 with MATE 1.26.0 It used to be that clicking on a PDF opened it with Atril. I don't know what *I DID*, but it now opens with L3afpad.
I assumed that Edit Preferences was the place to go.But under Browser->Helper Applications it says "always ask" indicating system isn't getting that far.
I used to know what to do ;< Help please.