Hi! You do not need to buy another Office, all retail versions (the ones bought from MS store or retail stores) can be activated on 2 computers. office can be reinstalled and activated on the 2 systems any number of times like in case of HDD failure,
viruses or just reinstalling the OS. this is allowed only for non-commercial computers. (http://www.makeuseof.com/answers/move-microsoft-office-2007-desktop-computer-laptop/)
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