What part are you stuck with?

From the module documentation, it seems it wants to get the HTML and then can render that into PDF.

As you already seem to have a way to produce the HTML, for the conversion to PDF, you would just do that:

1. Produce the HTML
2. Convert it to PDF
3. Output the PDF to the user

It would seem to me that step 1 is unlikely to be the problematic step as you say you already have the HTML.

So which one of step 2 and step 3 is problematic, what code have you written and how does it fail to produce the appropriate output?