Hello
Following the loss of the source files, I am looking to reproduce a box (with a complex/rounded shape) from STEP.
I managed to export a 3D sketch with the edges and I wonder if it's possible to give it a thickness.
The 3D sketch shows the outer contour.
If a good soul passes by, I'm taking advice.
Item4.SLDPRT (64.7 KB)
Impossible for me to open the file:
Ditto 
It would be better to provide us with the step in order to see what the project looks like.
From the 3D sketch, you make portions of surfaces (extusion / revolution / boundaries) you " sew" them and if all the surfaces end up forming a closed volume, SW will propose to transform it into a solid