With OEM machines, (computers from retail or manufacturers that arrive with Windows already installed), if Office is pre-installed it is usually a Trial Version for you to test if you wish and purchase if you like it. The trial usually lasts for 60 days, after which much of the functions of the trial software is disabled.

If your computer arrived with the Full Version of Office installed then you were entitled to the Office CD. If you didn't get that, then you need to contact the computer supplier for it.