Quick one : does Rakarth's action (new DE hero from Sign of the stars b'pack) trigger Sorcerers Convent action?
Does forcing opponent to put a card from his hand is considered as 'discarding card from hand' despite the fact that the card doesn't land on discard pile?

Nope. Rakarth's action isn't considered to make the opponent discard a card, so it can't trigger the Convent's action.