For those wondering, the HTML Help used by the app is actually generated from a (non-public) TBX. I developed a secondary export method that generates a single, styled HTML page. That is then post-processed to fix HTML TB inter-note links to HTML in-page anchor links. Finally wkhtmltopdf is used to generate the PDF.
The overall process is described here; although written for v5 the same principles hold, if you’re keen to try this sort of think with your own projects. If so, and you have question, please start your own thread in the Export sub-forum.
Edit: updated URL to point to Eastgate website