So I bought a laptop off of ebay and long story short I need to return it.The only problem is I added personal files to the computer and I need to return it exactly how I got it.

Part of the reason I returned it is because it did not have a product key for Windows or for Office. I would like to format it so nothing personal is on there, however I can't because how do I reinstall windows and Office without product keys!?!?

So is there any way to format everything but whatever sectors hold Windows and MS Office?