Word documents looking weird

[Geert]

I'm sorry if the topic title is a bit vague, but so is the problem. Word is showing those L-shaped corners on the page in light gray. Additionally, all type appears to be smaller than should be. Also the space between the lines is larger than normal. The problem is that I can't change this behavior. Line height and font-size settings are all normal.

A small screenshot is attached. Does anybody know what is going wrong here? Thank you.