Unfortunately, in this case, starting with Office 2013, Microsoft has changed the way they handle Microsoft Office product key, only storing part of the product key on the local PC. For instance, you can extract the Windows product key through the Windows Registry.
Based on product key search results, finding an Office product key is not as easy as the Windows one. Have you lost the Microsoft Office product key? Things may happen when you plan to reinstall Office to a new PC, or encounter a computer crash, etc.
