Convert STL/OBJ to STEP file 3d model

I have an existing part saved only as an STL mesh and I need it converted into a clean, watertight solid that I can use directly in engineering analysis software (ANSYS, SolidWorks Simulation, Abaqus, etc.). The STL must become a true parametric model—STEP

Key points
• Start from my supplied STL.
• Re-surface or re-build so the file opens as a solid body, not a mesh.
• Preserve every dimension and detail; no simplification unless we discuss it first.
• Deliver the final file ready for import into FEA software without further repair.

Please let me know which CAD platform you prefer and roughly how long you’ll need once you see the mesh. If you have past examples of mesh-to-solid conversions for analysis, feel free to share a screenshot or two to speed up selection.