I experienced a behaviour I've never seen before when opening, editing and saving a PDF today. As soon as save the PDF with Preview the file will be password protected, and I cannot open it again.
I've tested this on multiple files, but it seems to only affect files that have an "administrator password" set.
Test files from the Swedish Social Insurance Agency: https://www.forsakringskassan.se/wps/wcm/connect/b581c10a-8782-4c84-8448-4a469b85422b/fk7457-004-f-002.pdf?MOD=AJPERES&CVID=&CACHE=NONE&CONTENTCACHE=NONE
Is this behaviour somehow by design? I've never seen it before, and at first I suspected that some kind of malware caused this. But now I'm not so sure anymore.
I'm using macOS Monterey 12.2.