How do you trade Pokemon from Pokemon Pearl to platinum?

Answer 1

go to any Pokemon center, got to the 2nd floor and talk to the lady at the first door. you will have to save the game. go in with your partner and talk to them, select trade and the other person must accept trade offer. once you have done that the trade will be started.

hop the helds=p

Answer 2

Here are the steps,

1. You must have 2 Nintendo DSes - unless you want to do it the risky way through the GTS but it's better to use 2 DSes for trading between games though.

2. You must have the PokéDex.

3. You must be in the Union Room in both games. It's upstairs in any Pokémon Center, it's the left room that's up there.

That's pretty much all you need to know in order to trade between the 2 games.