The first is “viewable but not editable” — supposedly what you are using now. This is, by necessity, a very simple lock, else you could not read it.
The second is “only open with a password”, and that has much stronger security. But then you need to know the password as well.
PDF security is no stronger or weaker than just about any software security, and that, in turn, is not “better” or “worse” than the lock on your front door: it keeps out the occasional door knob jiggler, but it does not guard you against a determined burglar with a crowbar.