Thanks a lot specter for your feedback.
Maybe it's me, but when rendering in Wireframe mode, and then when I convert the .lin file to a bitmap file, I can only get a full wireframe image. As I said, I want an Hidden Line image.
I think I checked every possible setting. The only way I found so far to generate a bitmap file of a Hidden Line wireframe is with what Urp said previously.
I tried what you said, the Tools > Line > Show File, and it gives me a full wireframe image.
I tried the various standalone applications, like lin2pic and lin2eps. The lin2pic gives full wireframe image, and the pic2eps does not work, no matter what (we tried Photoshop and many Illustrator versions, on Mac and PC, and never been able to open the generated eps file).
So your help is really appreciated guys, and I'll appreciate too any other idea.
Bernard