You can add digital signature in the app an then apply it to your scanned documents.
To add a signature - tap on a scan to open it on the screen and then tap pen-like button in the low left corner of the screen:
This will open Edit menu where you will be able to see various options. Sign option is the last to the right (see a screenshot):
Tap it and then tap Signature button - you will be forwarded to the next screen, where you need to create a signature by simply signing the screen of you device:
Tap Done when finished and the signature will be added to your app’s signature library:
Now you will be transferred to your scan where you will see signature placed on it:
Move the box around the document for the correct placement of the signature. After this simply tap anywhere outside of the signature box and you will see the document with a signature added.
To edit or remove the added signature - quickly double tap the scan to access Editing, then tap on a signature once to activate the box around it and tap X button in the top left corner of the box: