It depends a lot on the nature of the html document you are trying to convert. One simple way is just to use the Word automation to open an .html document and then save it as a .doc document.
object readOnly = false;
object isVisible = true;
object missing = System.Reflection.Missing.Value; // Values we don't care about
object fileName = "C:/webpage.htm";
object newFileName = "C:/webpage.doc";
Microsoft.Office.Interop.Word.Application word = new Microsoft.Office.Interop.Word.Application();
// word.Visible = true; // To see what's happening
Microsoft.Office.Interop.Word.Document document = word.Documents.Open(ref fileName, ref missing, ref readOnly, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
document.Activate();
object saveFormat = Microsoft.Office.Interop.Word.WdSaveFormat.wdFormatDocument;
document.SaveAs(ref newFileName, ref saveFormat, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
document.Close(ref missing, ref missing, ref missing);
Note
- You have to add a reference to Microsoft.Office.Interop.Word or something similar
- The number of ref missing arguments depends on wich version of Word you are using
- You have to use full paths in the filename as the Word instance starts from the System folder.