Consider dynamic convertion docx to html using powertools (or even using office VSTO, it will be fast) and then using wkhtmltopdf (directly or with pechkin or similar) to render png from html.
I've wrote why wkhtmltopdf is better then for ex. iTextSharp here.
By the way, I think that the best commercial library to work with doc/docx is TxText - its really awesome, you can do anything you want.
