The headline feature is XHTML to docx conversion, formatting it based on the CSS. Images and tables are supported. See ConvertInXHTMLDocument and ConvertInXHTMLFragment for example of converting entire XHTML documents and fragments respectively.
There is heaps of sample code here (freshly reviewed for 2.8.0). If you are interested in using docx4j, grab a copy from the release link above, then see the "Getting Started" guide, in html docx or pdf flavours.