Originally Posted by Italophile

Once you have recreated your QAT as you want it you may want to make a backup copy in case it goes missing again, or you need to transfer to another pc. Just make a copy of the file in a safe location and if you need to restore it just copy it back to its original location, replacing the existing file.

The file to copy is named Word.officeUI and you can find it in %LOCALAPPDATA%\Microsoft\Office\