If you are going to convert a file in Alibre/ Geomagic as a DXF or DWG file you need to make a drawing of it first. If you are just using a solid model. If you draw the file In Geomagic you can use the "export file feature to export the solid model In any of the following files Step(stp), IGES (*.igs), Acis, stl ,Sldprt ,jpeg .
How did you get the file from Netfabb to Geomagic did you import it as a dumb solid?
I just looked at the Nettfab program, it would appear that the only files common to both programs are STL files
So if you can import an acceptable model into Geomagic , you should be able to edit that, then export it in one of the file formats listed.
B.E.

You are judged not by what you know, but by what you can do.

berkshire, thank you for your reply!
I just don't get what drawing you mean. Do I have to make a completely new drawing?
I want to convert finished .stl file to another format using Geomagic.
Is it possible at all?

In Geomagic when you open your model, at the very top left corner of the feature tree, there will be a title of your part. If you right click on that title, a fly out will offer you two options (Color properties) and ( Make drawing of this design.) Select the make drawing of this design . The drawing wizard will then assist you in making a 3 view drawing of your design, that you can then save in AutoCad format .
I very strongly recommend going back and reading the Geomagic tutorials.
B.E.

You are judged not by what you know, but by what you can do.

berkshire, thanks again!
I'm totally new to Geomagic and can't find the feature tree you're talking about - I use Geomagic Studio 2012, does it make diffrence?
I used this vid as a tutorial when I tried to convert the file myself https://www.youtube.com/watch?v=zDvg3QS60Mc, but something went wrong anyway.

Bavdeyka.
To do what you want to do, you need Geomagic Design not Geomagic Studio. You can download a free trial version from their site The current version is version 16.0.2 I think the trial version is good for about a week.
B.E.

You are judged not by what you know, but by what you can do.