I am unable to close this window, so I can't Unlock the PDF nor Cancel. I can't close the Preview app or view and edit other files, as this pop-up just doesn't go away. So, I am not able to shut down my device as well. Can anyone tell me how to fix this issue? Thanks in advance.
The PDF might have caused the app to be irresponsive, although it doesn't happens so often. Try to force quit Preview app. Press option + command + esc
Refer to this article: How to force an app to quit on your Mac - Apple Support (IN)
Just in case the force quitting of app didn't work for you. Force restart Mac
PDF owner password
