From a client i received a .u3d file.
How can i import it in Blender or is there a converter to change the type.
I found a website that says that it’s possible to read such a file in blender,
but not how to import.
http://fileinfo.com/software/blender/blender
Who can help me.
I know this is a very old post but I found the answer 
so for future guest Final Mesh opens u3d and saves to lots of common format dae, fbx, obj or 3ds
http://www.finalmesh.com/
additionaly I was looking how to extract 3d object from pdf? If somebody needs it, here is the answer: pdf-parser.py usage