Installed Catalina, now I can't open files. I checked permissions, I have read and write permission. Help!

Try resetting permissions: Resolve issues caused by changing the permissions of items in your home folder - Apple Support

It could be something related to permissions, but not specifically the POSIX permissions you see in the Get Info window.

What happens when you try to open them?

Any error messages?

Where are the files stored? In your Home folder or somewhere else?

What program is set to open them? Can you open the files from the Open command in the default app?

I have a similar problem (Pages, Numbers, Keynote). I restart the machine and the problem goes away.

Unfortunately it is not a permanent fix and every few days the problem re-occurs. System restart sorts it out.

I think it is something to do with cases not being cleared.

I am not using Safe Mode simply doing a system restart.

Hope this helps.

YIKES!!! Having the exact same problem again!!! Is there a permanent fix out there? @Barney-15E

It would probably involve removing whatever is altering your permissions. It is not normal for that to occur repeatedly. If it does, I would assume something is causing the problems. I don't know what that might be, though.

Could be MalwareBytes, or any other type of utility.

MBAM is a tool for removing Adware that you installed, either willfully or accidentally. Unless you enable its scan function, it is doing nothing to prevent you from installing more adware. If you have it set to scan, it could be the cause of the corrupt permissions. I've never set it up to scan, so I don't know what it is capable of doing.

Anything that provides any modification or enhancement to the OS could cause the problems.

Miss typed should read "clearing caches".

Thanks Barney-15E, the link to Apple's 'changing the permissions' support page appears to have resolved my issues!!