I am often asked what is the best way to synchronise files, and the answer to this is to save them on iCloud Drive.
iCloud Drive allows you to access and edit the same document on multiple devices. Many refer to iCloud as a backup, but it is important to understand that it is not.
If you delete a file on iCloud then it will remove it from all of your devices. The only true backup is through Time Machine on a Mac. However, if a device is lost or stolen, your files will still be available on your iCloud.