I'm having the same problem on Mac running Catalina: After upgrade to Evernote V 10.4.3 , on my desktop application PDF are not shown ("couldn't display this PDF file"). Also, thumbnails are not shown, JPG and PNG are not shown ("image could not be rendered properly").
I can see them in the browser application, and on my android phone. Things were fine until the update 2 days ago.
I uninstalled and reinstalled, doesn't make a difference. This applies to ALL the files with these formats, rendering Evernote basically useless. Sinvce I do not have premium, I can't send a ticket.