[MBAtarga]

Is this to reproduce what I consider that retro/vintage look for a house front door with 3 small windows diagonally placed across the upper portion of the door? (edit - your post and picture appeared after my question)
If using a router - I'd cut a template for a pattern following router bit of the appropriate depth and clamp it to the door in each of the three positions.
The other option would be to mark the cutout positions and use a jig saw (Bosch or equivalent). As someone above posted - I'm assuming the cuts do not have to be perfect, as the "window" trim would cover the edges.