AutoSketsch R10 / Windows 7, 64 bit
If i have saved a drawing file into skf-format it is inpossible to save a copy in dwg-format.
If in my AS (v9), Save-As options include: (Quote)
AutoCAD 2000 DXF (.*DXF)
AutoCAD 2000 Drawing (.*DWG)
AutoCAD 2004 DXF (.*DXF)
AutoCAD 2004 Drawing (.*DWG)
AutoCAD R12/LT2 DXF (.*DXF)
AutoSketch v7/v8 (*.SKF)
Autodesk Design Web Format (*.DWF)
Windows Metafile (*.WMF)
V10 must ‘at least’ have the above, .. I would have thought. (?).
I don't have 10 handy at the moment, but from memory it does the same as the above formats (might also have AutoCAD 07 but I'm not certain).
However I find DWG unreliable (some things don't save, some programs complain about opening them) and use DXF.