PDF files won't open with either Preview or Adobe

After updating to Sequoia 15.7.3, now when I try to open any PDF file on my iMac desktop using Preview I now get the following error message and the file won't open:

"(Name of file.pdf) can't be opened because the identity of the the developer cannot be confirmed."

I have tried solving the problem doing the following:

1. Restarting in Safe Boot. (Still happens)
2. Reinstalling operating system. (Still happens)
3. Deleting the "com.apple.Preview.plist" file in the "/Library/Containers/com.apple.Preview/Data/Library/Preferences/" file. (Still happens)

It is NOT happening on other users accounts on the same computer.

Why would Preview, which is an Apple application be doing this?

Any help, please!