Open the "Tools" menu and select "Open User Directory" to find the memory card storage.

To unlock all characters in for PC, users typically use a save file (often in .psv or .mcr formats) that has already completed the game's requirements. This bypasses the need to play through the Arcade and Tekken Force modes multiple times to unlock hidden fighters like Dr. B or Gon. How to Get a "Best" Save File for Tekken 3

The "best" save files are those labeled "100% Complete," which include all characters, all extra costumes, and all ending movies unlocked.