At the last job I worked at they had a shared folder. In this folder they would put scanned documents. The only problem was sometimes they updated documents or created new sub folders.
This script will copy all updated files, over writing the previous ones using the date modified as a comparison. It will also copy subfolders to the backup destination as they are created.
It will not delete files if the name of the file has changed.
Now this script is a little complex, but if you follow the instructions at the bottom, you should be fine.