Something here may help.
https://support.microsoft.com/en-us/office/using-product-keys-with-office-12a5763a-d45c-4685-8c95-a44500213759?ui=en-us&rs=en-us&ad=us
or try this (or similar) tools.
https://www.nirsoft.net/utils/product_cd_key_viewer.html
https://www.belarc.com/products_belarc_advisor
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