When Disinformation Campaign enters the battlefield, you draw a card and each opponent discards a card.
Whenever you surveil, return Disinformation Campaign to its owner's hand.
An ability that triggers “whenever you surveil” triggers after you’re done surveilling, even if you have fewer cards in your library than the number of cards you’re instructed to surveil. It even triggers if you have no cards in your library.
Disinformation Campaign’s last ability triggers only if it’s on the battlefield. It won’t return from your graveyard.