Yes, you can delete it.
Note: Please be sure to verify your saved file on the external drive before you delete your original one.
Make sure it will read or play back correctly.
It would be easier if you do the save as when you are going to save your file,
You would prompt the program to save it to the WD external drive instead of the internal computer.
That way when you need it, all you need to do is to prompt the program to open the file from the WD external drive.
Using the WD Smartware program is also fine but it would be a little bit complicate.
You would need to do several steps before you reach the file you need.
You would either retrieve it first before you can use it.
Or you can prompt the program to open it from
WD SmartBackUp/YourComputerName/Users/Documents/Users/UserName/Documents/Name of Your File.