This happens because the PKG is encrypted with a content key. The RAP file contains the decryption key. Your console checks the /dev_hdd0/exdata/ folder for a matching RAP file. If it finds one, the game unlocks permanently. If not, you get an error.
To use these files on a console, you must have an active mod like Evilnat CFW Step 1: Preparation Format a USB drive to Create a folder on the root of the USB named Place your files inside the Place your files on the of the USB (not in any folder). Step 2: Installation Plug the USB into the right-most port of your PS3. Enable HEN (if applicable). Package Manager Install Package Files Select and install the Step 3: Activation pkg rap ps3
A RAP file is the required to unlock the content within a PKG. Most digital PS3 content is encrypted. Licensing: It acts as the license (rif/edat) for the game. Small size: These files are tiny, usually only 16 KB. This happens because the PKG is encrypted with a content key