I believe the OP is referring to the existing Source Hunter DLC that converts basic copies to the CE version.
In which case, why don't you (referring to the OP) just read the description on the Steam store page?
Unlocks Divinity Original Sin: The Golden Grail DLC, Divinity Original Sin: Zandalor's Trunks DLC, Divinity: Original Sin Design Documents and Art Pack, and Soundtrack.
In game items:
Golden Grail - Add a gold sheen to your wearable items to increase their value with vendors.
Zandalor's Trunks - Heckles you while you play the game. Also reads gravestones aloud.
Out of game items:
Design Documents and Art Pack/Soundtrack - I'd say these are pretty self-explanatory.