No. You need the password to open the file. Think Pages doesn't guess or crack passwords.

Yes. Some PDFs open without a password but block printing, copying or editing. Opening the file here removes those limits, and the copy you export has none.

No. The password and the file stay in your browser on your device, and the password isn't kept after the file is opened.

Yes. Every tool asks for the password when you add a locked PDF, so you can merge, sign or convert it straight away.