By default, Notebooks stores your documents in a predefined local folder on your device, or in a predefined folder on iCloud Drive. The Custom Storage Locations option allows you to select any folder on your device, on iCloud, even on a connected USB device or on a network share. You can create new folders and switch between existing folders, and thus rotate between separate sets of documents.
To give an example: you can use a shared iCloud folder with documents for your team; select a different iCloud folder for private documents; keep another set of documents in Notebooks‘ default location and synchronize that with Dropbox; yet another set of documents resides on a removable thumb drive for use on your iPhone, iPad and Mac.
Selecting a Custom Location
When you choose to switch to a custom storage location from Location settings, Notebooks displays a standard iOS file and folder selection dialog. This dialog provides access to local folders, to iCloud Drive, connected devices and network shares. This is where you can create new folders or select existing ones. As you select a location and close the dialog by tapping Done, Notebooks switches to that folder (“location”) and displays its contents as books and documents. All additions and edits you make apply to the files and folders in that location.
When Options in the File Selector Are Grayed Out
The file and folder selection dialog may also show a list of applications like Dropbox, Boxcryptor, OneDrive and others. These are so called cloud storage providers, acting as interfaces to data stored on a cloud service. In the dialog they appear as regular folders, but they are applications controlling access to documents stored elsewhere. The fact that these applications appear in the list suggests that you can select them as storage location, but in most cases you cannot; most of these providers do not allow Notebooks to access their folders. Selecting a specific Boxcryptor or OneDrive folder might be tempting, but this is currently not an option, unfortunately.