RTF to HTML .Net is a cross-platform .NET library that allows your applications to convert DOCX, RTF and text documents to HTML 3.2, 4.01 + with CSS, HTML5, XHTML 1.01. After adding a reference to "SautinSoft.RtfToHtml.dll" and entering 3-4 lines of C#, you can use the API in your applications:
HTML 3.2, HTML 4.01, HTML 5, XHTML with and without CSS. All HTML documents created using RTF to HTML .Net are fully compliant with W3C Markup validation service standards.