How can I send to CC book formats with a type (extension) calibre doesn't recognise?

Some people use calibre to manage items that aren't standard ebooks, for example audio books and recipies. These "books" usually have a file extension that calibre doesn't recognize, making them difficult to send to CC

Starting in calibre 3.12, the Wireless Device driver in calibre has a preference where you can list these "extra" formats (extensions) that you want to be able to send to CC. You can add these extensions in the Wireless Device (SmartDevice) configuration. To access that configuration:

1. Start calibre.
2. Go to the driver's configuration screen.
   Alternative 1:
   1. Connect CC as a wireless device.
   2. Click the down arrow next to "Device" on the tool bar.
   3. Choose "Configure this device"
   Alternative 2:
   1. Go to calibre Preferences
   2. Click Plugins (at the bottom of the dialog)
   3. Search for SmartDev. The "SmartDevice App Interface" plugin should be automatically selected
   4. Push the "Configure" button.
3. You will see a box at the bottom of the configuration dialog with the label "Additional file extensions to send to the device".
4. Enter a comma-separated list of extensions you want CC to accept. For example, some audiobook extensions: m4b, aax
5. Press OK.
6. If CC is connected as a wireless device, disconnect.
7. Connect CC as a wireless device so calibre can tell it about the extensions.
8. Disconnect.
9. In CC, go to Settings / Formats and folders. The new extensions will be in the list but not selected. Select them and move them to the priority you wish. You might also want to put them into a folder different from where you keep your "normal" books, especially if the app that can handle the files changes them in some way or extracts information from them.
10. CC will now accept those extensions from calibre.