Use and Buy Product Key Online For Windows 8.1 Windows 8 and other software and operating systems installed on your PC required the entry of unique product keys or serial number when installing them. This key will be with the email confirmation that you’ve received after you buy a product key for windows 8.1 online or download or with a packaging case you get it in a retail package. More details : https://www.keyshoponline.com/product/windows-8-1-pro-key/