Hello Alexey,
Thanks for your reply.
When I import my fbx in AutoCAD, the message "The file cannot be imported because his format isn't supported" pops.
My mesh is not that much big cause it is a 1300k vertices one with a 30k, 4 bands and uint8 texture.
If it may help, I tried to export other meshes in fbx and the result is exactly the same, the format seems to be unsupported.
Thanks by advance.