Backup files are zip files containing your documents. To import a backup file from GoogleDrive, OneDrive, Dropbox or Box, please tap on the + button in the upper left of your library view in GoodNotes and select the respective cloud storage. Please note that you will need to tap the Select button in the lower right to import multiple documents at once. Currently, folders are not supported, which is why you will need to restore your categories separately.
If you are importing a backup file from iTunes please remember to connect your device to your computer via USB.