I’m trying to cut a rectangular hole in my cube. You can download my source file on this link. The cube was tempered with subdivision modifier and and the shading is smooth. This is what I got so far:

I used the left block and a boolean modifier to cut a hole. The problem is that I need my hole to be exactly the same shape as block-right angles are necessity. The Blender gives a warning that my boolean modifier is not the first one and that results may not be what I expect. So how do I cut a block hole out of the object with smooth surface? This really bugs me and I’m very thankful for your help.