From Adam Swiderski’s “A History of Copy Protection” (Edge: 9 June 2008):
Fortunately, the games industry is creative, and thus it was that the offline copy protection was born and flourished. One of its most prevalent forms was an in-game quiz that would require gamers to refer to the manual for specific information – you’d be asked, for example, to enter the third word in the fourth paragraph on page 14. Some titles took a punishing approach to this little Q & A: SSI’s Star Command required a documentation check prior to each in-game save, while Master of Orion would respond to a failed manual check by gradually becoming so difficult that it was impossible to win. Perhaps the most notorious example of this method is Sierra’s King’s Quest III, in which lengthy passages of potion recipes and other information had to be reproduced from the manual. One typo, and you were greeted with a “Game Over” screen.
Other developers eschewed straight manual checks for in-box tools and items that were more integrated into the games with which they shipped, especially once photocopiers became more accessible and allowed would-be pirates to quickly and easily duplicate documentation. LucasArts made a name for itself in this field, utilizing such gems as the Monkey Island series’ multi-level code wheels. Other games, like Maniac Mansion and Indiana Jones and the Last Crusade shipped with the kind of color-masked text one would find in old-school decoder rings; the documents could not be reproduced by the photocopiers of the day and would require the application of a transparent red plastic filter in order to get at their contents.