A common occurrence in business is the electronic signing of an agreement. The tools below allow you to quickly scan a paper document and email a pdf version of it using a mobile app, and add signatures to an existing pdf using a desktop application.
Mobile Scanning App
Available in both the Google Play and the iTunes stores, Notebloc allows you to quickly take a photo of all pages of a paper document, then email a pdf. I literally went from installing the app to taking the photos, emailing the pdf and receiving it in a matter of seconds. A real nice feature is that after you take the photo, the app shows it to you with handles on the corners and sides of the scanned image. If the photo is somewhat distorted then you just drag the smart handles to fit the edges of the document. The app then creates a remarkably clean, rectangular version of the page with no background. I tried this with paintings and the result was also very pleasing.
Desktop PDF Signing App
Adobe Acrobat PDF Reader
You can download the free Adobe pdf reader, then enable the Fill & Sign feature to sign and save the pdf to your local machine. When you enable Fill & Sign it steps you through a quick wizard where you select a font for your initials and signature that most closely fit your own handwriting. From that point forward you just select Fill & Sign, then click the Sign item in the top toolbar to place your signature, initials or typed text into your document.