More often than you might imagine… it has been necessary while sailing to fill in and/or sign documents and scan / email them. Some countries like Fiji and Australia require visiting sailboats to fill in complex/long documents and send them in advance of arrival.
We found this piece of software a couple of years ago and it has just gotten better with each upgrade. Tiny Scanner is intuitive and does a great job for us. You can use it handheld on your iPhone or iPad… but if you have multi-page documents to scan… we found that it is easier to mount the i-device on a tripod.
You will note that the camera is not directly over the paper. This is not necessary as the software corrects for these types of parallax errors.
Note: The HP printer in the photo is battery powered and has done a great job for us… but it is several years old now and I suspect you can find better units now.