The magician shows a deck cut diagonally. Stretching out the two halves onto the table shows how the cards are completely different in both piles.

The cards are turned over to the back and two spectators are invited to choose a half-card from each pile that lies before them. The two half-cards are brought together and shown as backs fit together perfectly.
Magically when the two halves are turned also faces coincide, composing a whole paper.

Being a bunch rigged and manipulated is not shrink-wrapped.