Apps to draw on top of a picture or text document? What apps can be used to draw (like with a finger or stylus) on top of a text document or a picture?

What I envision is being able to send a document to the app (or take a picture/scan the document if necessary and load the image) and then be able to sign in an appropriate place with a finger, and then save/email/print the resulting document.

I would have thought something like Evernote would do this, but apparently not.
Skitch (same developer as Evernote) can draw on top of a picture, but not on a document.