How did they do this magic trick?

I always go on this cruise boat that's called Discovery and always go to the showroom. In the showroom they they do magic tricks and stuff. There's this Magic trick that fascinates me, it's called What A Coincidence, or something like that. It goes like this: first a magician has a newspaper and an envelop. Then the magician would pick a volunteer to come up and pick any word from the newspaper and say the word out and the magician would open the envelop and the exact same word that the volunteer said is the exact same word that is in that envelope. And the magician would be like "what a coincidence, that's the same word I wrote in the envelop." How did they do that magic trick?????