It can't. Stl are mesh formats. It has 3d points and triangles to define the shape. CAD formats are different and can't be created from meshes. For example you create an arch instead of a sharp corner, CAD knows it's an arch and you can change the radius later or just delete the arch and it will give you the sharp corner. In a mesh an arch is just a series of lines, the software doesn't know about any radiuses, etc. CAD software can export to stl meshes. They then approximate the object with 3d points and triangles.
You can manipulate meshes in sketchup or meshmixer for example.
Many CADs can import meshes and display them in 3d but they can't modify them with their usual tools. Then you can design your cad object using the mesh as reference.