Take all his pads and put them right by the door, then when he's used to that, move it outside.
Don't leave any pads inside, potty pads are a bad habit.. and also I think its gross :/ Gets smelly often etc., if he has to go, he has to go outside, but leave the pads outside at first,only outside , when he gets used to them, then take them away
Eventually he will get this and do his buisness outside.
Don't forget to say ''no!'' to him if he does something on the floor inside, and go straight outside with him.
Good luck
!