How to convert docx to html file using open xml with formatting

I know there are lot of question having same title but I am currently having some issue for them I didn't get the correct way to go.

I am using Open xml sdk 2.5 along with Power tool to convert .docx file to .html file which uses HtmlConverter class for conversion.

I am successfully able to convert the docx file into the Html file but the problem is, html file doesn't retain the original formatting of the document file. eg. Font-size,color,underline,bold etc doesn't reflect into the html file.

Here is my existing code:

public void ConvertDocxToHtml(string fileName)
{
   byte[] byteArray = File.ReadAllBytes(fileName);
   using (MemoryStream memoryStream = new MemoryStream())
   {
      memoryStream.Write(byteArray, 0, byteArray.Length);
      using (WordprocessingDocument doc = WordprocessingDocument.Open(memoryStream, true))
      {
         HtmlConverterSettings settings = new HtmlConverterSettings()
         {
            PageTitle = "My Page Title"
         };
         XElement html = HtmlConverter.ConvertToHtml(doc, settings);
         File.WriteAllText(@"E:\Test.html", html.ToStringNewLineOnAttributes());
      }
    }
 }

So I just want to know if is there any way by which I can retain the formatting in converted HTML file.

I know about some third party APIs which does the same thing. But I would prefer if there any way using open xml or any other open source to do this.