Default style
You can assign a style for all the paragraphs meet during the conversion. Of course, the style attributes on the tag are still applied over the specified default style.
In this example, the
Intense Quote style is used.

C#
converter.HtmlStyles.DefaultStyle = converter.HtmlStyles.GetStyle("Intense Quote");
Html
<h1>A title</h1>
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Duis dictum leo quis ipsum tempor nec ultrices sapien elementum.
Some texts does not apply the expected style
If you add this line of code in the startup example and run it again, you will not see the "Heading 1" style applied.
In fact, the "Heading 1" style is well applied but this style does not exists in the document ; when you create a new document, no styles are defined : it's up to you. HtmlToOpenXml handles automatically the hyperlink style for you but it does not deals with any others.
You can subscribe to the StyleMissing event to be warned and add them yourself.
converter.HtmlStyles.StyleMissing += delegate(object sender, StyleEventArgs e)
{
Console.WriteLine(e.Name);
};
Generally, you will load in memory an existing document template and append the Html conversion inside it. MS Word 2007 embeds a lot of informations (like styles, themes, document properties, ...) that you don't really want to bother with.