Hello everybody. My name is Dayna Martin, working as a Technical Support assistance for Microsoft products and services. Some users are confused about the use of a Microsoft Office 365 product key. These users are mostly people with less technical knowledge. When you go to www.office.com/setup and download Microsoft Office 365 or subscribe for it, you will need the product key. The product key will be required so that you can install the required files on your computer. The product key is asked by the PC while installing the Microsoft Office files.