If Unlock DLC.zip is a zip file containing files meant to be placed into a game directory:
Right-click the game > Manage > Browse local files Steam Support . Unlock DLC.zip
Download and install JDownloader , a Java-based download manager designed to handle container files. If Unlock DLC
Scenario 1: A Compressed Archive ( .zip containing game files) Unlock DLC.zip
JDownloader will decrypt the file and add the download links to the link grabber list.
To make sure I'm giving you the right steps, could you let me know: Is it a or a .dlc file extension? Which game is this for?