The «Documents» folder contains installed maps and charts. They are stored in the «MapPackages» subfolder.
The maps can be backed up to a computer and copied to another device. However, commercial maps are protected with a certificate that will only work on the device where it was created. If you try to install maps on a second device, you will have to do it through the section «All my products» located in the «Map Store» module to create the certificates.