The only way I have found that this could be done was to generate printed documentation, PDF it, add it as a baggage file to RH and link that PDF file. Users can click on the PDF file and print the entire thing. What I am looking to do is allow users to either print an entire book from the TOC or be able to print multiple topics at once. I'm using RoboHelp 9.
I agree the most convinient way to Print your complete content can be with Printed Documentation (doc/pdf). If you have a button, the print would happen to the topic in focus from TOC.
What is you default output format?