Can´t find my CD Key

[jose.joao.tata.jogos]

Hello everyone,
So, i've bought LEGO® Harry Potter: Years 1-4 a few years ago in a game store, wich means i have the box with the actual CD of the game. I whanted to be able to play the game withough having to always use de CD, so i though of transfering it to steam, but in the box i can´t find the CD key to activate it.
Is there a way to find the CD key in the instalation or something? Or somewhere on Steam where i can get the key and activate the game, after showing proof that i actually bought the game?

[Waschbärpfötchen]

The original game released years before it got a Steam release, sadly meaning you can't activate your original copy on Steam.

Btw. it's currently on sale.