California Association Of Realtors (C.A.R.) Forms

No you must remove the lock, with or without the password, to be able to sign.

You should ask Google how to unlock a PDF for free in the blink of an eye.
It's a piece of cake.

It depends what kind of "lock" it is. Could you share a sample file?

And there's no such thing as "signature tags", so what they wrote doesn't make much sense.

You can apply a digital signature using fields, a certificate or something like Adobe Sign, though.

Or you could apply an "analog" signature using an image file or even one of the commenting tools (like the Pencil tool), but that has no real meaning and can be easily faked and duplicated.