Load your STL into a mesh editor like (free) or Netfabb .

There are several reasons why you might need to convert SDF to STL:

Converting a parametric or mesh model into an STL file, which is the industry standard for 3D printing slicers (like Cura, PrusaSlicer, or BambuStudio). The STL format represents a 3D object as a shell of many small triangles (tessellation).