stl2rsdocx v1.0

Open STL, 3MF, OBJ, DXF, and STEP files in the free tier of DesignSpark Mechanical — no subscription, no install.
DesignSpark's free Explorer tier won't import these formats (they're locked to the paid Creator tier). This tool converts them into the formats Explorer does open, so you can view your parts — and rebuild many of them as editable solids — for free.
Download: grab stl2rsdocx_gui.exe below, double-click, done. Windows only; nothing is installed.

⚠️ First run: Windows SmartScreen may flag it as from an unknown publisher — click More info → Run anyway. Normal for unsigned tools.

What it does

STL / 3MF / OBJ → clean mesh you can view in Explorer (.rsdocx)
STL / 3MF / OBJ / DXF / STEP → editable rebuild curves you Fill / Revolve / Blend into a real solid and save as .rsdocx
Smooth seams — hides triangle lines for a clean view
Drag-and-drop, batch convert, hover tooltips on every option

Good to know

Smooth-seams output is view only — use a Rebuild-curves mode to get something editable.
Flat, round, and prismatic parts rebuild well; genuinely twisted/organic shapes don't (that's paid-Creator or FreeCAD territory).
STEP supports analytic/prismatic geometry (planes, cylinders, cones), not B-spline/organic surfaces.

See the README for the full how-to. Not affiliated with RS Group / DesignSpark.