The concept of a "PS3 to PS4 PKG Converter" is a common misconception in the console modding community.
Directly converting a PS3 game into a PS4 PKG (Package) file for native play is not possible
You redeem a code included with your PS3 disc or digital purchase on the PlayStation Store
Features to Look for in a PS3 to PS4 PKG Converter
Folder to PKG Conversion
: Transforms "JB folders" (standard PS3 game backups) into a single, installable PKG file format.
