For those who want to go the extra mile and print the game manual/booklet for the DVD case, you can often find a PDF of the game's manual on Steam.
If you own the game you can go to the game's page in your Steam library and click the "Manual' link on the far-right under the "LINKS" header.
You can also find it on SteamDB by searching for the game, clicking the Information tab on the left, and clicking the link in the "GameManualURL" row.
If steam does not have a manual for the game, then the mentioned links will not exist.