Mostly the results will not be great.
Going from 3D geometry (for example STEP) to STL is easy, but loses information. Going back in the other direction is complex - many conversions just replicate the facetted STL as a STEP - giving huge file size compared to the original CAD definition. So the result is unwieldy and difficult to edit.
A few systems try to re-create a proper CAD definition of the original geometry.