Yes you are correct.
You would need to preform a template override, please see:http://www.jevents.net/jevents-15-topme ... jevents-15
With the defaultviewhelperheader16.php in the JEvents views helper folder.
I have not used it in JEvents as it is a very specialized request.
Furthermore, I am not sure how PhocaPDF would handle JEvents CSS / HTML.
You could alternatively use google chrome and its built in PDF Printer. Enable printing in JEvents, click Print and the page comes up to print. Just click Print to PDF. But this will only be able for you to generate a file and not for all your users.