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.
Prefer typing? Choose the Type tab, write your name and pick a handwriting style. Or use Upload for a photo of your signature.
Tap on the page where the signature should go, then drag and resize it. Tap Lock if you want it to stay fixed.
When finished, tap ⬇ Download at the top to save the edited PDF.