It uses official Steam API data to see what achievements exist for a game, then watches your local emulator folders to see when you've met the criteria.
Alternatively, use scripts like generate_emu_config.py to create these files manually using the game's Steam AppID. how to get achievements in pirated games
To use a trainer or Cheat Engine:
If you’ve finished a pirated game and later buy the legitimate version (or just want to sync your "offline" progress to your public Steam profile), is the go-to utility. It uses official Steam API data to see