I have a Mac that runs on OS X Yosemite 10.10.5. I got this computer from a friend.  It did not come with a product key or disk for MS Office. I can use Word, Excel & Powerpoint but when I try to open Outlook I get:  "This account isn't associated with this office product.  If you purchased Office for yourself use the same account that you used when purchasing Office.  If you received Office through an organization or school please contact your administrator.  If you have a product key, go back and select Enter a product key instead."  I am no longer on good terms with the friend I got the Mac from.  How can I get a product key so I can get into Outlook?