I work at Expected Behavior, and we've developed an HTML to PDF API called DocRaptor. DocRaptor uses Prince XML for PDF generation, and we use HTTP POST requests to create PDFs.
You can try this example:
http://docraptor.com/documentation/examples_php
However, this requires the pecl_http extension, so it may not work for you. In that case, you could try this wrapper one of our users wrote:
https://github.com/krewenki/php-docraptor/
DocRaptor is a subscription-based service, but we also have a free plan that allows users to create up to 5 documents per month at no cost. All plans have a 30 day trial, and you can create unlimited test documents.
I hope this helps, or at least provides an alternative for you.