If you're unable to find your product key, you can contact Microsoft Support for assistance. They may ask you to prove your purchase to verify the product key.
: Many "cheap" keys sold online are Volume Licensed keys intended for businesses. These may work initially but can be deactivated by Microsoft later if they violate terms of service. Modern Alternatives product key for ms office 2013 top
Unlike later versions of Office that attempt to link themselves automatically to a user's Microsoft account, Office 2013 relies heavily on this specific string for validation. It tells the Microsoft servers that the software running on your computer is legitimate, licensed, and not installed on more computers than the End User License Agreement (EULA) allows. If you're unable to find your product key,
: You can find the last five digits of your installed product key to verify which license you used by running a specific command in the Command Prompt as an administrator: These may work initially but can be deactivated
: If you purchased Office online, sign in to the Microsoft Store or your Microsoft Account Services page to view your purchase history and keys.
Finding a legitimate requires a mix of digital forensics (checking your Microsoft account), hunting through old emails, and physically inspecting ancient COA stickers. The "top" method is always the one you already own—retrieving a lost key from a past purchase.