Hi,
I want to subtract the surface of a small rounded solid to a bigger surface of a rectangle, in order to have like a hole in the latter. I tried the Boolean difference the but it failed.
I have attached a screenshot that shows the two surfaces and the 3dm file.
Most often these are done using closed objects; it will work on two planar surfaces if they are exactly coplanar - use SetPt Z only, to force these to be colplanar. Note as well that surface direction matters when Boolean operations involve open objects like this. (Dir command). The normal direction will determine what happens in a Boolean.
See also the Trim, Split, and CurveBoolean commands.