Ok, in wildfire, after you done the dinamic analysis you have to reproduce it, clicking the icon "play" and select the analysis you have done.
Then click on the last icon on the top right of the windows,where you select the analysis.
In the new window select the quality of the solid generated (1 is verypoor,you can try 6-7),click on the black arrow and pick the component you want to do the envelope (by default all the component od the assembly are selected).In the bottom of the window, you can see the output format;click on part or part PL, and fill the name in the box (if you don't like the one that is given by default).
Click on Preview or directly on create.
The part is saved in the working directory. If you want to assembly in the generic assembly to verify, i suggest to use the coordinate system.