If you bought the box product at a store, the product key can be found in the packaging.

Check all mail folders including the Junk folder for this email. If you purchased from a third-party retailer try searching the retailer's name. If you purchased Office 2010/2013 directly from Microsoft, search for 'Microsoft' in your emails. You may also be able to recover the Office product key in the confirmation email you received if you purchased the product online.

The account details page will contain the product key and provide a download link to install Office. To recover the product key, go to Microsoft's My Account and sign in with the Microsoft account tied to the install. This option is available if you purchased, downloaded, and installed Office 2010/2013 online, or at one point, the product key was associated with a Microsoft account. You may be able to recover the Microsoft Office product key online. If you bought the box product at a store and you haven't installed Office 2016 yet, the product key can be found in the packaging. If you continue to have problems signing in to your account page, contact Microsoft support to review your options. If you sign in to your account page with a Microsoft account that's not linked to your subscription, you'll get this message: ' Office isn't associated with this account.' You'll need to sign in with the Microsoft account that was used when you redeemed and installed Office for the first time.

Microsoft 2013 product key