Originally Posted by
NightrainSrt4
If the acrylic isn't too thick then I would just blast through it with a rotary tool cutting disk and file it smooth with a hand file. You can still do this with thick acrylic, you just have to be careful that the melted acrylic doesn't form around the disk and cool back down, otherwise you risk cracking the acrylic if it happens at a narrow spot.
I'm not sure I fully understand the second question. If you have a square hole in the side panel, if you put that up there, then you would have holes in the window where the negative space is. If you just want a window to show through with the shape you are showing, then you would just use a square piece of acrylic behind the door panel and cut the shape into the door panel instead.
Welcome! If you give some more information about what you are trying to do, we can give a bit more help. =)