Good morning. First post. Just upgraded to Catalina y'day and its been a disaster. Brief history: a week ago i received a pdf that would not open. said it was encrypted. had never seen that. assumed the file was the problem - had been protected or similar. But the guy said he'd only protected against edits. So ...??? A week later i receive another pdf from a different source, and same error message. So, now the problem looks like on my end. I suspect that my old Acrobat Pro (2008) was simply too old to open this file by a newer Acrobat. Tried to upgrade Acrobat, but turns out my O/S is too old for Acrobat 2020. So i try to upgrade the O/S and Apple steers me straight to Catalina. OK, Fine. So i do that yesterday, but it starts taking forever. I mean hours. And when it was finally complete, so many things seemed screwed up. My Mail app said something like it had been wrecked and i had to re-install it or something(?), and so then it set about downloading 78000 emails.... for several more hours. In addition, none of my old apps work with the new O/S so I lost all my Adobe Creative Suite, MS Office, and others. But basically, the computer is running like its in quicksand - essentially unusable. One cant sit waiting 23 seconds to switch between tabs on Chrome, or 17 seconds for an email to open. What could be wrong? Wondered about the memory, the harddrive has about 500GB of space, and the iMac has two 4-GB RAM chips (?)... Any ideas?