In your case a possible reason of an appearance of a blank page, is a page content exceeds given page height and followed by a page break directive (most probably “page-break-before: always” CSS property; possibly tag).

So alternatively you may suppress/override page-break-before style (with pd4ml.addStyle() API call, for example)

But if the issue is the same with a variety of your documents (page content does not fit only few pixels), obviously the page layout has been developed for a smaller content scale. You can scale down the content by an increasing of htmlWidth parameter.

See http://pd4ml.com/cookbook/pdf_page_formatting.htm