If you purchased and downloaded Office Setup from an online store, the product key should be in your email receipt.
How to Find Microsoft Office 2010 Product Key Confirmation Mail?
Check your spam, bulk, or junk mail folders for the email.
Try searching your email for the word “Microsoft” or the name of the company where you bought Office.
If you have multiple email accounts, check the email account that you provided when you purchased Office 2010 online.
If you can’t find the email receipt, you may be able to retrieve the information contained in the email by using the Order History link for the store you made the purchase from.
How to View your Product Key if you Purchased Office from Digital River:
Go the Digital River download information page.
Select Find my product key and enter the information requested to download software or get your product key.
Get your Office here: office.com setup
How to View your Product Key in the Microsoft Store:
Go to www.microsoftstore.com. In the upper right-hand corner, select Sign in and enter the user ID and password you used to buy Office.
After you sign in, select your name in the upper right-hand corner, and then select Order History.
Locate the Office one-time purchase or individual Office app, and then select Install Office to view your product key.
Note that this product key won’t match the product key shown in My Office Account. This is normal.
For more details, visit : www.office.com/setup.