If Office 2013 is already installed but you've lost the paper record, you can retrieve the of the key to help identify it: Open the Command Prompt as an administrator.

: If you bought a retail box, the 25-character key is located on a card inside the packaging. Activation & Changes

on April 11, 2023. While you can still find product keys through third-party retailers or retrieve existing ones from your Microsoft account, the software no longer receives security updates, posing a risk for modern systems. Microsoft Support How to Find or Retrieve Your Product Key

Never underestimate the power of a physical DVD. If you bought a boxed copy of Office 2013, the product key is inside the DVD case, often on a yellow or orange card. If you have the disc but lost the card, check the back of the manual or the inside of the sleeve.