Thanks for the comment Zax.
I am still defining a route from 3D modelling to the laser cutter.
At this moment the route is as follows:
1 Create 3D model in Autodesk Inventor.
2 Create drawing of model in Inventor
3 If needed, add extra engraving lines in the drawing manually.
4 Save the Inventor drawing as DXF R12 file.
5 Use QCAD to explode all objects (hatches, text) to polylines
6 Save the QCAD drawing as DXF R12 file.
7 Import the DXF in T2Laser
8 Create NC
Although it looks a long way, this isn't really the case. 25% of the steps are done automatically with some home made code. The inventor drawing contains hatches which will be translated as separate lines. (step 5) This way I can create custom hatch patterns which follows the borders of surfaces automatically when I change the size of these surfaces in 3D. Same goes for text blocks.
The things I am struggling most with are the settings in T2Laser. This has to do with my lack of experience of the software.

Last night I was halted by another setting behavior. (I think) I have a DXF file (Thanks for the sugestions Zax, I dropped the PDF route here) which contain colors at line level, not on layers!
After the DXF file (step 7) the colors are shown correctly. (Huray!) But when I create a nc file, I see all power values are set to 255. And I wanted to control the power of the laser by these colors.
DXF options set:
on - Engrave and Cut
on - Absolute DXf colors , 0 (I have read the line in the manual several time but don't understand what this value does?)
on - Force Splines
on - Reverse DXF segments
on - Skip minimum power
on - Combine path
The preview only shows one color, blue. Shouldn't this be all the colors which are also visible when open the dxf file?
The NC doesn't have any speed corrections, all are 255. Why?