Hi Bastien,
The available file format for Layout files included in the design files is the layout .brd file included in the LAY-29102_C1.zip directory of the KW41Z's Design Files Archive:
<…\FRDM-KW41Z_C2-DESIGNFILES\LAY-29102_C1\LAY-29102\LAY-29102_C1.brd>
I'm really sorry for the inconveniences this may cause.
Best regards,
Sebastian