As mentioned, Inkscape exports dfx files which can be imported to shapr3D however to get really smooth shapes (import as proper curves) I’ve found you have to do the following:
select text
Path → Object to Path
Object → Ungroup (each letter will now have a dotted box around it)
Save as AutoCAD DXF R14 (not R12!)
if you get a dialog box with options, deselect ‘use ROBO-Master’ and ‘use LWPOLYLINE’
Well, oddly, I went to make a simpler test case with a single letter and I was seeing smooth curves with both export options. I saved over the not-smooth one when I re-exported with the other options, so sadly I don’t have it any more.