You can fill out forms and sign documents that you receive on your iPhone. After you complete a form, you can add your signature and share it with others.Simply open the PDF file on your iPhone or iPad. If you're prompted to save the document in the Files app, choose a folder and tap Save. This video will show you how to sign documents with the iPhone and how to sign PDF on iPhone. Go to the Notes app on your iPhone. In a note, tap the Attachments button , then tap Scan Documents. 1. Open Notes and select a note or create a new one 2. Tap the Camera button, then tap Scan Documents 3. Tap on the camera icon then Scan Documents.