In the age of widescreens, Windows offers a really helpful function for viewing documents, or just play pranks on your friends. With a simple key-combination, you can rotate your screen into any direction - flip it upside-down, or lay it on the side:
To rotate the screen, press Ctrl + Alt + Arrow key. The arrow you press determines what direction the screen will be turned. This feature is useful especially if you can set your screen resolution to fill the screen while it lies on the side - flip your monitor on the side afterwards and you've got the perfect size and resolution for viewing documents.