A quick google lead me to LeoCAD, which exports 3DS and OBJ, both of which can be opened in C4D.
And there's a video or forum thread somewhere that says you can import LDD files into LeoCAD, but I dunno why you may want to do that, since LeoCAD seems to do what LDD does anyway.
Then again I don't know anything about Lego in 3D, so maybe LDD has stuff leocad doesnt :/
either way, Hopefully that helped!
Pour le coup il y en a plusieurs ! Lego Digital Designer doit etre le plus connu et gratuit
LeoCAD, a l air bien
Stud.io est le dernier en date il me semble
Actually with LDD you can print your own pdf instructions without going to the lego site. It would appear that LeoCad uses lcd files.
I just installed it and have not yet had a chance to try. Looks like you have to download your brick sets.
The first message I got when trying to open LeoCad is
LeoCAD could not find a compatible Pieces Library so only a small number of pieces will be available.
Please visit http://www.leocad.org for information on how to download and install a library.
So a little bit of reading to do.
Some years ago I used LeoCAD to build models in this way:
I would download the manuals to old lego sets that I always wanted as a kid, but never had, and then build them with this tool.