Microsoft patents a technique to display encrypted documents so only you can see them
If you're working on an important document in a busy environment and don't want people to see what you're doing at a glance, then you could use a privacy screen on the display or an application that dims areas not in your gaze. Microsoft has patented a system that it believes is superior to both because it makes the document fully encrypted and illegible at all times—apart from the section you're directly looking at on the display.
