word files not opening in iis

private void DownloadTemplate(string FileName)
   {
       try
       {

           String strFile = String.Empty;
           String[] filename;

           strFile = Server.MapPath(ConfigurationManager.AppSettings["TemplatePath"].ToString()) + FileName;

           filename = strFile.Split('\\');

           Response.Clear();
           Response.Buffer = true;// Read the original file from diskFileStream *
           Response.AddHeader("Content-Disposition", "attachment; filename=" + filename[filename.Length-1]);


           String ext = String.Empty;
           if (strFile.IndexOf(".") > 0)
               ext = (strFile.Split('.'))[1];

           if (ext.ToLower() == "txt")
               Response.ContentType = "text/html";
           if (ext.ToLower() == "xls")
               Response.ContentType = "xls/html";
           if (ext.ToLower() == "pdf")
               Response.ContentType = "application/pdf";

           ////combine the path and file name
           if (File.Exists(strFile))//open the file and process it
           {
               FileStream sourceFile = new FileStream(strFile, FileMode.Open, FileAccess.Read);
               long FileSize;
               FileSize = sourceFile.Length;
               Response.AddHeader("Content-Length", FileSize.ToString()); //*
               byte[] getContent = new byte[(int)FileSize];
               sourceFile.Read(getContent, 0, (int)FileSize);

               sourceFile.Close();
               Response.BinaryWrite(getContent);
           }
           Common.UserPageAudit(Session["User"].ToString(), "Download Templates", Session["ROLE"].ToString(), strFile + " Template downloaded");
       }
       catch (Exception ex)
       {
           Response.Redirect("../CustomError.aspx?Err=" + ex.Message.ToString(), false);
       }
   }