On the Home screen, tap one of the 5 big cards: Scan with Camera, Sign a PDF, Password Protect, PDF Converter or Extract Text (OCR).
Tap Choose file and select your PDF from the phone or computer.
Choose Remove password and type the password you already know. Only unlock files that belong to you.
Tap the big purple Start button and wait a few seconds.
When you see Done!, tap Download. The new file is saved on your phone or computer.