How can I make/create drawings of my STL files?

Creating drawings from STL (or OBJ, PLY, etc) files is not trivial as these formats are based on facets (basically using triangles to approximate the shape) while most/all Mechanical CAD applications use Boundary Representation (BRep) as a way to define the geometry.
When importing mesh files, several applications will take the shortcut and simply represent the triangular originals as flat surfaces bounded by three straight lines. This works, but results in what you are seeing (I think SW may even have a limit set on the number of facets it supports).
At this point I would provide you with a link to the software my company has developed to help (though not necessarily always fully resolve) this issue... but I won't, unless specifically asked, as it was called out as spam by another user previously. You can also search online for other applications that similarly allow you to reverse engineer the data you have, this should generally result in a cleaner body (again: not always).
But the bottom line is that you need to rework or otherwise resolve the triangles in the model, otherwise your CAD application will consider the bounds of the facets/triangles as actual edges and show them in the drafting/drawing environment (where you may be able to hide them individually/manually).
Hope this helps....

Ótima resposta do Ben!!!!