For those not familiar with 3D PDF workflows I will outline a few instances where they are useful for you as a user of Cinema 4D.
If you are a professional user, or freelancer, by incorporating 3D PDF documents into your skill set you could open up a new revenue stream for yourself and also help boost your clients workflows in the process.
Creating Digital Assets for a Client
You may be creating a model for a client. By saving out as a PDF file you can send the model to the client for them to look at. They can add notes directly into the PDF file itself to tell you what parts to change, what camera views they would prefer, and what additions to make on the model. They then simply save the pdf and send the file back to you. When you open the file you will have access to all of your clients notes and their saved camera views. Your clients will be able to view, and edit, the PDF using the free version for Adobe Acrobat Reader. No need for any other special software or a copy of Cinema 4D at all. Only Adobe Acrobat Reader.
Creating Marketing Material
Companies may want something more than just a 2D brochure for their clients. By incorporating 3D models into the PDF documents your clients will be able to show their users what their product really looks like by allowing them to navigate around in full 3D. You could incorporate high resolution product renders of the product as well as a full 3D model for people to have a look at and get a closer look. What does that Shoe look like from a different angle, how does that watch look really close up etc…
Creation of 3D Training Material
The Automotive and Aerospace industries use PDF files heavily in their workflows for creating end user documentation and training materials. Being able to show users the parts of an engine and how it works, in 3D, is much more intuitive than trying to work out a bunch of 2D technical drawings. 4D Publish will supply more tools to help with this workflow in future to allow easy creation of product documentation and training material.
Similar to the above example, you could work with clients to create 3D Educational material to help students learn about many subjects. A map of the human brain, parts of an engine, internal workings of a cell, navigation around a city etc…
I hope these small examples help you to get a feel for what could be done by introducing PDFs to your workflows.