Remember, you're getting into dangerous territory here if you start uploading your creations made from decompiled models.

HOWEVER:

You need to import your dxf file (note that you can also download free dxf models from websites) into your design program.

Most probably, the dxf mesh you import has:


all parts sharing the same 0,0,0 axis point;
no animations,'
no textures assigned,
no eye candy features,

plus the models you can decompile are older format models that probably do not have all the animated parts you would want anyway.

You have to finish the model in the design program and then export using the export feature of your design program (gmax or fsds)