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.
Tap Sign. On the Draw tab, sign inside the white box with your finger or mouse. Clear erases it. Then tap Use.
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.