This is the download link to Microsoft Office 2011. According to this document, the product key was mailed to you in a mail with subject 'Microsoft Office for Mac – Order Confirmation'. The whole activation procedure is described in Office for Mac 2011 Activation and Product key Information (via ). If you aren't sure which site to use, you can enter your product key using the Virtual support agent (English only). First, make sure that you're entering the key correctly on the right site. You probably don't own a legitimate copy of the program) I'm afraid you're out of luck, I believe the licensing information may be stored in the .plist file which is located in /library/preferences. Depending on where you bought Office 2011, you can retrieve the product key from Microsoft using the instructions on their website. In the Get Started wizard, click Enter your purchased product key.

Find your product key for Office for Mac 2011. If you have a one-time purchase of Office for Mac 2011, you’ll need a product key to activate.