Document Scanner, CamScanner -Phone PDF Creator, Adobe Scan, Clear Scanner: Free PDF Scans, Document Scanner - PDF Creator, Fast Scanner : Free PDF Scan so on.
None of those apps have a back up feature?
How do you back it up to your desktop or save the scan document to your desktop? Does apps give you that feature? If some thing happen to your phone or tablet you could lose all your scan documents. Or if some thing happen to the app you could lose all your scan documents.
Does the apps not give you the ability to scan documents to SD card or your desktop computer.