SkyDemon is really a good flight planning tool and it would make the application even better if one was able to save the flight plan in FSX/Prepar3D-format
Regards
Kennet

How would that make it better? Can you describe the situation where a pilot would wish to import data in those formats so we can understand the requirement?
I'm guessing FSX is the simulator but I have no idea what the other tool you mentioned is.

I'd suggest using this... http://www.flightutilities.com/FPonline.aspx

To convert the output from SkyDemon into a .PLN file which FSX (and presumably Prepar3D) will accept.

(Prepar3D is a commercial spin-off of FSX by Lockheed Martin)

When I create a flightplan in SD I would like to be able to use them in P3D (Prepar3D) "directly" as a training aid.
SD is such a nice flightplanning tool and I would like to be able to use it in both worlds - live and training.
I do think that the xml scheme is the same for FSX and P3D.

Don´t think that FPOnline generates a XML scheme that FSX and P3D accepts.
Only FS9 in text-format, I  believe.
I have not found any converter that does what I want.
So, I have started to build a simple converter (in C#) from the SD .gpx export to .pln for Prepar3D.
But the SD .gpx export is only rudimental, so...

Working on a flightplan converter for prepar3d from the SD GPX export.
It seems that the GPX xml scheme cannot be validated.
When I try to generate C# classes I get the following error:
The 'http://www.skydemon.aero/gpxextensions:level' element is not declared. Line 21, position 28.