Owner password required to unlock this PDF
I downloaded a PDF from internet some days ago, a book for uni. I edited it, underlined something, you know the drill. Today I was going to open it but a window asking for a "owner password" appeared from nowhere. So the PDF is now encrypted. But why? By who? Originally, it didn't ask for any password. I was able to do whatever i wanted. How can this still be an issue?
Always used the Preview app, nothing from third part.
MacBook Air 13″, macOS 13.3