Viewer Pane problem with pdf files

Recently, when I try to see a pdf file with the Viewer Pane, the system hangs for a couple minutes and then shows a very long list of "machine code".
I upgraded to Version 12.8.
The problem persists.
Thanks.

Your PDF viewer is broken and may need reinstalling.

Presumably PDF viewer in is also not working in Explorer's viewer pane?

Some suggestions are here, but I would first try just reinstalling whichever PDF viewer you use, as that often solves the problem.