ShopReady Draft 3D · 1:10 · narrated, with captions

An STL brought in, changed, and written out as STEP and 3MF

A plate with two holes arrives as an STL file, which is only triangles. File, Import a solid brings it in; Measure shows that the round holes are round holes again (the mark finds a hole's center) and the flat sides are flat faces. So the Hole tool works on it as on a part made here: a third hole is added, 6 across. Then File, Export writes it for another CAD program as STEP, and for a slicer as 3MF.