It's next to impossible to answer this question without knowing what software you have available on the PC.
In professional software such as Photoshop, it's relatively easy to do. Furthermore, are you talking about an illumination on a plain page or on something resembling a photograph? It really does make a difference.
On the other hand, if you have MS Word, make sure the Drawing Toolbar is displayed. One of the buttons on the toolbar is called "3-D". Click on it and at the bottom of the menu that opens, you should see a menu that says "3-D Settings". This opens a small toolbar, on which is something that looks like an anglepoise lamp head. Click on this. This will provide you with a limited directional light beam to direct upon objects on the page - it's not fantastic but it may be good enough for what you need.
You could also try some of the free Serif software downloads, some of which I think can do as you ask.