What does Owner password mean for your PDF?
A file with only an owner password opens with no prompt at all. What you notice is that Print is greyed out, text refuses to copy, or a form will not accept typing.
The permission flags sit inside the encryption dictionary: print, copy, modify, annotate, fill forms, extract for accessibility, assemble and high-resolution print. Readers are expected to respect them, and most do.
Because the document itself is readable, clearing the flags is a matter of rewriting the file rather than breaking encryption — no password required.
Why can restrictions be cleared without knowing the password?
Because nothing is hidden. The pages of a permissions-only PDF are readable by any program that opens it — the flags are a note in the file asking readers to behave, and readers comply as a courtesy. Writing the same pages into a new file simply leaves the note out.
This is not a flaw that was overlooked; it is the design. A document that everyone can read cannot also be cryptographically prevented from being read. Only a user password does that, and it is a different feature.
Which is worth remembering when you rely on restrictions to protect something. They stop honest use in ordinary software — a colleague who cannot print, a form that will not accept typing. They stop nothing else.
Clearing restrictions on a document you have no right to redistribute is still a copyright question, whatever the file allows.