Document Scanner allows you to scan documents with your phone camera, convert them into PDF, and email or share the PDF document to anyone, all from your mobile phone.
This App also has a Sign Feature.

You can scan any number of pages and convert them into one single PDF file. You can even add to an existing set of scanned documents.

The app also includes cropping. This app will select the four corner points of the document (with manual adjustment possible as well) and correct that image. It will also automatically crop at those points to reduce your file size. You can also adjust the grayscale as desired, or convert the document to black & white