Use Markup
Add a signature to a scanned PDF
For a simple signature on a scan, Notes and Markup are a practical starting point.
Start with Apple NotesFreeExplore Apple Notes 
Do this
- 1Open the scanned document in Notes and select Markup.
- 2Use Add, then Signature, and create or choose your signature.
- 3Position it on the page, finish, and share a copy.