Thanks for your inquiry. I am afraid currently Aspose.Pdf.Document(DOM approach) renders HTML document to PDF document, but it does not support to add HTML contents(inline) in PDF document at the moment. We have already logged this feature request as PDFNEWNET-35804 in our issue tracking system. We will update you via this forum thread as soon as it is resolved.
Thanks for your patience. As stated above PDFNEWNET-35804 is resolved and now you can add HTML string in new/existing document using new DOM approach. Please check following documentation link for the purpose. It will help you to accomplish your requirements.