For new installations, product keys for Microsoft software are found either on the retail DVD or in the confirmation email if the product was bought through the Microsoft store. To retrieve the product key for an old installation, key-finder software may be necessary.
Microsoft Office software stores the product keys in the Microsoft Registry, but the keys are encrypted. As a result, they are only read by key-finder software. Microsoft Office 2010 has a unique product key for activation, so the product key needs to be available in either the physical copy or on the confirmation email. A key finder program may work to find the product key in the registry.