my pvc door lets in rain, but i can't find were it's coming in?

i have a double glazed back door that when it rains hard the carpet inside gets soaked, i have read about checking the slits are not blocked, and testing by pouring water over them. but being a woman, i'm not sure where these are located, There is a pvc bar that runs across the door at the end, is that it? and does it come off? Also i'm surei can feel a bit of a draught at the end, could it be the seal?

Any help on above i would be grateful of

Ellen bham