The card is imprinted face down. This means that other players don’t know what the card is and you can’t look at the card once it’s imprinted (until it’s turned face up, of course). Note that effects that exile cards, including all previous imprint cards, exile those cards face up unless the effect says otherwise.

Any “When this creature is turned face up” abilities that the exiled card may have don’t trigger because the card isn’t being turned face up while it’s on the battlefield.

If the card is not a creature card when it’s turned face up, it remains exiled face up.