AlphaPixel recently delivered a Free/Open Source 3D PDF generation/conversion tool for exporting models to the PRC format and embedding them into PDF files.
Based on an OpenSceneGraph Reader/Writer plugin, and open source PRC code taken from the Asymptote, the osgdb_prc plugin converts the geometry, material colors and transparency, and in a limited fashion, the per-vertex coloration of models into a PRC file. This file can be embedded into a PDF file using the libHaru toolkit. The final result is a PDF that can be opened in modern versions of Adobe Reader on any platform, where the model can be viewed in 3D and interacted with.
Existing structure in the OSG scene graph (groups and node names) are preserved in the PRC file, exposing the graph structure in Adobe Reader where subsections can be drilled down into and shown/hidden.
AlphaPixel, with the authors of the Asymptote PRC code, is working to publish a fully independent PRC library using the PRC code currently hosted in Asymptote.
The OpenSceneGraph PRC exporter and forked PRC library code is currently hosted on GitHub at https://github.com/XenonofArcticus/libPRC