Microsoft Office 2013 in VirtualBox

So, I'm a fairly new Ubuntu user, apologies if I'm missing something easy here. But I have installed VirtualBox running Windows 8.1 Pro x64, attempting to install Microsoft Office 2013 x64. When I click the setup application I get the error message "This app can't run on your PC. To find a version for your PC, please check with the software publisher." I had Office 2013 on Windows 8.1 before I switched over to solely Ubuntu and it installed fine.
Any others have the same issue or is it simply not workable?
Thanks.