Unlocking removes the password from a PDF you already have the rights to, so you can open, edit, print or merge it freely without entering a password every time.
ColaPDF removes the protection in your browser, but only from files you can already open — you must know the current password. The tool is designed for convenience with your own documents, not for bypassing security on files you do not own.
Yes. This tool removes protection only when you already know the password.
No. Everything runs in your browser.
The tool will show an error — no file will be produced.