So the attacker has to have exploits in every pdf reader app on linux? Since it is not Adobe only and there are quite a few. Or maybe a common backend engine (mupdf and popler)...
I heard a story from years ago that security researchers tried leaving USB thumb drives in various bank branches to see what would happen. They put autorun scripts on the drives so they would phone home when plugged in. Some 60% of them were plugged in (mostly into bank computers).