there are two options:
The first one is to add a texture to your board
a) export the Front Silk gerber file with pcbnew (you can replicate it also for front Cu)
b) convert gerber to png with gerbv (gerbv — a Gerber (RS-274X) viewer - Browse /gerbv/gerbv-beta at SourceForge.net)
c) set transparent background for the png
d) use the png as texture for your board (this works in FreeCAD)
The second one is more tricky
a) set pcb thickness to 0.1 (design rules-> layer setup-> board thickness)
b) export VRML from pcbnew
c) remove your shapes3D folder or move the file to a different place
d) import this VRML (pcb, tracks, silk) in your MCAD and put it over the board (this works in FreeCAD)
@xavierw please let me know if one of these can work for you
it should be PTC Creo (ProE)
Maurice