Acrobat 3D and Adobe Reader, Version 8 and later, include support for 3D Annotations®. So you can embed 3D CAD models within a PDF, and explore them interactively through manipulations available in the default toolbar.
Creating 3D Annotations
Developing Plug-ins and Applications, Version 8 (PDF, 4.6M)
Learn how to programmatically create 3D annotations in PDF files using the Acrobat SDK or the PDF Library SDK.
Acrobat 7 Professional contains a new 3D Tool, which allows you to embed U3D objects in a PDF document. After this 3D model is embedded in a PDF, it can be distributed and viewed by anyone with Acrobat or Adobe Reader 7.x.