I tried the 3 solution proposals that were made to me:
Coyote: I did some research on DataKit but all their solutions are paid for (at full price) and I don't want to incur any additional costs...
Ac Cobra 427: same answer as for DataKit...
Mick.Cordero: Having a Premium license I activated the ScanTo3D add-on, but when I register under "3DS" I get the following message "There is no entity to process in 3DS." and I don't know how to make it work (and yet I have read a good part of the online help...!?)
I think I know why, in fact, a 3DS file is a "mesh" file and I think you directly export your model from a volume or surface body.
The solution is as follows:
Export your file in STL format (the default stl, the one that everyone has even those who don't have Scanto3D, not the stl of Scanto3D because you'll end up with the same message)
Import your file with the Stl type but from Scanto3D this time, you'll see, it's at the bottom of the list in "mesh file"
Finally, export your file in 3DS format, this should no longer be a problem.