A product key is a 25-character code used to activate a Microsoft Office 2013 product. It's usually required to install and use the software.
If online activation failed (e.g., no internet), users could call Microsoft’s automated phone system. This two-factor approach (key + hardware ID) was designed to prevent casual sharing of keys across many devices. microsoft 2013 product key
A single-purchase option tailored for users who want to avoid recurring monthly software subscription invoices. A product key is a 25-character code used
$$Product\ Key = SHA-1(Hardware\ Hash * License\ Key)$$ microsoft 2013 product key