3 ways to check and see MS Office 2016 Product Key

You may have to reinstall or install Microsoft Office 2016 on your computer and during the installation, you will be prompted for a 25-character product code. If you have a license key for MS Office 2016, enter it in the text box to complete the installation.
Find and view the Office 2016 product key with the tool
If these methods do not help you find your Office 2016 product key, try using the - Cocosenor product key.

1. Download Product Key Tuner.

2. Double click on the file "cocosenor-product-key-tuner.exe" to install it on your computer and select launch now.

3. Click the Restore Restore button, and then all the Product IDs and Product Keys are displayed as below. And the Office 2016 product code can be viewed clearly in the list.

read more here:MICROSOFT OFFICE 2016 PRODUCT KEY