How to cut a curved surface?

Hello, I can't find a solution to this.

I want to cut a part (i.e. to create an rectangular hole in a part), following the surface.... I want the hole with the same deep in every point.

I tried to sketch in a plane and project the sketch on the Surface, that become a 3D Curve, but I can't cut a Surface with a 3d Curve.

I treid also other features but no one worked.

Thanks for the help