Office for Mac was not updated for last 4 years. Latest Office for Mac which you can buy is Office 2011. Its is now very primitive and use to crash a lot too while doing intensive task as pivot table. Microsoft had already updated Office not only for Windows platform, but also for iPhones and iPads. Finally they are giving away a preview version for Mac 2015. Which you can download by clicking here. Its 2.5 GB download, which contents word, excel, power point, one note and outlook.
Hopefully Microsoft should release a stable version soon and should make it free 😉