Open the file in PowerPoint, as opposed to running in Powerpoint. You will see the trick.

Look at the two picture - before and after.

Before:
Jack Diamond
Jack Club
Queen Diamond
Queen Club
King Heart
King Spade

After:
Jack Heart
Queen Heart
Queen Spade
King Diamond
King Club

None of the cards from "Before" is in the "After" picture. So when you can choose any card from "Before" and it will work.

The trick is that no one can remember all the details of all the cards in "Before", so it is easy to trick.