How can I find the product key of Office 2011 after restoring from backup?
This thread is a bit old, but in case someone else finds themselves looking for the answer, this just worked for me:
To move / re-install your licensed copy of Microsoft Office 2011 for Mac on a different computer / OSX installation, and re-authorize it without the license / serial / key available, copy the following from the old machine to the corresponding (same) spot on the new computer.
Please note that you should be looking for these folders in the root directory of the drive on which OSX is installed-- NOT in your user directory. To get there, in the Finder click Go--&gt;Computer--&gt;[name of the hard drive that has OSX installed...usually &quot;Macintosh HD&quot;]...then look for the following folders:

/Applications/Microsoft Office 2011 folder (copy the entire folder, with all its contents)
/Library/LaunchDaemons/com.microsoft.office.licensing.helper.plist
/Library/PrivilegedHelperTools/com.microsoft.office.licensing.helper
/Library/Preferences/com.microsoft.office.licensing.plist

From:
http://cwl.cc/2012/02/easy-way-to-move-your-microsoft-office.html
Note NOV2020: If you just copy/paste the last file &quot;/Library/Preferences/com.microsoft.office.licensing.plist&quot; as instructed above, it should work as well. For transparency, this was tested on an old mbp with El Capitan and incoming connections blocked with Firewall (unsure if Firewall would affect outcome).