Options for recovering a lost Microsoft Office product key including finding the key in the operating system registry of a computer on which the product was previously installed, finding it on a sticker attached to the product's DVD or CD cover or case, finding it on a sticker attached to the computer's case, or finding it in an old email from the seller. Another option is to contact Microsoft or certain Microsoft-authorized resellers such as Digital River.
For instructions on finding the product key in a computer's registry as of 2015, type "find your lost office key" in the search box near the top-right of the main page at HowToGeek.com, and then click the search icon. Click the link to the article "How to Find Your Lost Windows or Office Product Keys" near the top of the page, and then follow the instructions in the section titled "Finding the Windows Key Without Any Software."
If you purchased the product from Microsoft and certain other entities, you may have received an email that included the product key. Find the email by searching saved email from sources such as Buy.OfficeforMac.com, Try.OfficeforMac.com or DigitalRiver.com, or search for email containing text such as "Microsoft Office." If you still cannot find a product key, contact Microsoft by clicking the Contact Us link near the bottom-left of the page at Support.Office.com.