Ball rebounds from wicketkeeper's pads or body, can the batsman play it?

No, The batsmen can’t play the ball once it touched any players from the fielding side. Once it made contact with the wicket keepers pads it is called as a dead ball and is no longer in play.

you can refer to the rule

34.2 Not out Hit the ball twice

The striker will not be out under this Law if he/she

34.2.1 strikes the ball a second or subsequent time in order to return the ball to any fielder. Note, however, the provisions of Law 37.4 (Returning the ball to a fielder).

34.2.2 wilfully strikes the ball after it has touched a fielder. Note, however the provisions of Law 37.1 (Out Obstructing the field).

Here it can mean that he misses the ball and hits the keeper or hits the ball and the ball bounces of the nearby fielder.

And LAW 37.4 states

37.4 Returning the ball to a fielder

Either batsman is out Obstructing the field if, at any time while the ball is in play and, without the consent of a fielder, he/she uses the bat or any part of his/her person to return the ball to any fielder.