The spectator chooses a card and loses it in a shuffled deck. The magician makes a magical gesture and spreads through the deck fact up -- the selected card is gone!
The magician then reaches into a pocket and takes out a normal-looking wallet. In the wallet is -- the selected card!
The card is honestly chosen and returned to the deck. However, while the magician is thumbing through the deck to show that the selection is gone, a careful eye is kept on the cards. When the selected card comes up, the magician doesn't allow it to be seen but instead moves it along beneath the card on top of it as if they were one card. It appears that the card has vanished.
The magician now reaches for what people "in the know" call a Mullica Wallet. This wallet, named for famed German movable-type innovator Hans Mullica, contains a small stack of blank playing card stock as well as an ultra-thin set of printing plates that can be used to reproduce any card in a standard deck. With a few practiced presses of secret buttons on the wallet's surface, the magician causes an exact duplicate of the selected card to be printed. With a little advance planning, the magician can even have a plate duplicating a spectator's signature inserted in the wallet for a spectacular signed-card-to-wallet routine.
After the card is taken from the wallet, the magician shows it around (giving it time to dry) before giving it to the spectator as a souvenir. Because the real selected card is still in the deck, the magician is ready to perform again!