A file is the official installation format used by Sony for PS3 games, updates (including the famous "PS3_UPDATE.PUP"), DLC, and PSN (PlayStation Network) titles. When you download a game from the PlayStation Store, the PS3 downloads a PKG file in the background, then installs it to the console’s internal hard drive.

Before beginning the installation process, ensure your PlayStation 3 meets the necessary software and hardware requirements. System Requirements

A PKG file is a proprietary archive format used by Sony Interactive Entertainment for the distribution of digital content, including full games, add-ons, and patches.

Your PS3 must be running Custom Firmware (CFW) or PS3HEN PSX-Place.

Method C — Developer/debug tools