Windows 8 and 8.1 PCs no longer have a Certificate of Authenticity (CoA) sticker with their product key printed on it. This helps prevent theft people cant just glance at a sticker on your laptop to get your Windows product key. On the other hand, you cant simply look at a sticker on your Windows PC when you reinstall the operating system. Youll have to find the 25-digit product key elsewhere. Having your product key is necessary if you want to download Windows 8 or 8.1 installation media from Microsoft. Their downloads require a valid product key.