Artifacts you control have hexproof.
At the beginning of your upkeep, if you control the artifact with the highest converted mana cost or tied for the highest converted mana cost, draw a card.
9/20/2016 The artifact you control has to have the highest converted mana cost only among artifacts on the battlefield, not among all permanents on the battlefield.
9/20/2016 If an artifact has in its mana cost, X is considered to be 0.
9/20/2016 If you don’t control an artifact with the highest converted mana cost as your upkeep begins, Padeem’s second ability won’t trigger. You can’t cast an instant to destroy an opponent’s artifact during your turn before your upkeep begins.
9/20/2016 If you no longer control an artifact with the highest converted mana cost as Padeem’s triggered ability resolves, you don’t draw a card.