protected void ConvertToHTML(string docPath,string HTMLPath)
        {
             word.Application app=new word.Application();
             app.Visible=false;
             Object o=Missing.Value;
             object docFile=docPath;
             _Document doc=app.Documents.Open(ref docFile,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o);
             object fileName=HTMLPath;
             object format=8;//HTML
             doc.SaveAs(ref fileName,ref format,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o,ref o);
             object t=true;
             app.Quit(ref t,ref o,ref o);
        }

我放了演示程序在上面的FTP里，关于C#和office操作的更多信息，等看一下微软的白皮书了

Whitepaper: Using Microsoft office from C#

在www.gotdotnet.com上可以找到