Collapse the Ribbon to get more space on screen

When you need as much space as possible on screen to view a document, you can collapse (or minimize) the Ribbon to only its labels by double-clicking the label of the tab you're currently using.

Or press Ctrl+F1:

Minimize Ribbon in Word 2007

While the Ribbon is minimized, click any tab to turn it back on temporarily. It will automatically hide when you're done using it.

Display Minimized Ribbon in Word 2007

Double-click the current tab again or press Ctrl+F1 to expand the Ribbon back to its normal size when you want to have it displayed again.