How do you get a product key to activate Microsoft Word?

According to Microsoft, product keys to the Office suite of programs, which includes Microsoft Word, can be purchased from a Microsoft partner, reseller or at retail locations selling the product. All versions of Office require a product key except for the Office 365 Enterprise edition.

Activation keys consist of a unique code containing 25 letters and numbers. Activation of Microsoft Office requires an online connection as well as the product key. If a user loses a key, a replacement can be obtained by contacting the retailer, Microsoft partner or reseller that sold the user the original key, or by purchasing a new key.