Where is the 3D Model?
The 3D Model is actually inside the PDF. 3D PDF files are a standard PDF file, with the addition of an embedded 3D model, or “annotation”, visible as a 3D viewport. The actual 3D coordinates, shapes, vertices, polygons, lines, etc., are encoded in either a U3D or PRC binary encoding, stored entirely inside the PDF file. This can optionally be set to the PDF/E compliance subset. So it does not reference any external file, website or other software for 3D.