If you're thinking of just scriblling on the doc, the latest Acrobat Reader can do it, but if you mean of editing it, then you might need Adobe Acrobat or you might as well convert it to wordprocessing format first. Correct me if I'm wrong.
HP Envy x2 review: Hands-on
How Sketch and InVision have revolutionised our design workflow
The best tech gifts for Christmas 2017
Les meilleurs jeux de société (2017)