When trying to sign a document with Okular with a PGP signature on Windows I encountered the following issue when saving a file

Could not sign. Could not write to 'C:/Users/Carl/Downloads/mydocument.pdf`

Okular prompted me for a location for a file called mydocument_signed.pdf, so I am not even sure why it's trying to save at mydocument.pdf

Okular does create a mydocument_signed.pdf but when opening that file with okular, I am getting the following issue:

This document is digitally signed. Some of the signatures could not be validated properly.

And this is the result in the signature pane