The Level (Layer) content is not viewable in the PDF file (using Adobe version 8) created using the PDF plot driver file. There's no Level or Layer tab to select to view the layers inside of Adobe when creating a U3d PDF file.
A U3D file will not display the Level content.With Adobe Pro version 8 you can select View " Navigation Panels " Model Tree. (the location may be different for you if you are running a different version of Adobe). The Model Tree will allow you to turn On or Off pieces of the model.ehT