Open in another program

Hello.
I'm running into problems regarding deleting, moving or re-naming files/folders ... always PDF ones.
"...file is open in another program". There is no other program open!
In Task manager it sometimes works to end Adobe Collaboration Synchronizer (2), but sometimes the problem persists.
View is on List, so no thumbnail.
What program is the culprit? And just closing it every time - or even rebooting - is not a solution.
Is there a permanent fix?
Obviously I searched but with no avail.

Thanks in advance

Windows version 1909, latest .. always uptodate

Thanks Dalcina,
I will consider that.
However, I was hoping for a system solution since that should not happen. I see it more as a glitch about a program clinging to a certain file preventing it from being altered. This happens with no other files or folders usually and it shouldn't.
Is there a way of finding the core problem?

Klaus

Thanks,
I'll try it.
However, I'll leave it as unsolved hoping for more responses

Thanks