StreamWriter corrupting my RTF?

[chenw040]

Basically, I want the user to fill out a form and have the RTF file updated with those values and then emailed as an attachment.

My code is as follows:

System.IO.StreamReader reader = new System.IO.StreamReader(Server.MapPath("~/GrantProposal/text2.rtf"));
            string file = reader.ReadToEnd();
            reader.Close();

            file = file.Replace("gp1", frmDirector.Text);
            file = file.Replace("gp2", frmPhone.Text);

            System.IO.StreamWriter sw = new System.IO.StreamWriter(Server.MapPath("~/GrantProposal/text2.rtf"));
            sw.Write(file);
            sw.Flush();
            sw.Close();

            MailMessage mail = new MailMessage();
            mail.To.Add(emailTo);
            mail.From = new MailAddress(emailTo);
            mail.Subject = "Grant Proposal";
            //mail.Body = info;
            Attachment attach = new Attachment(Server.MapPath("~/GrantProposal/text2.rtf"));
            mail.Attachments.Add(attach);
            SmtpClient smtpClient = new SmtpClient("localhost");
            smtpClient.Send(mail);

When I test this, it emails the RTF fine, but when I download the attachment and try to open in Word, it gives me an error saying that the file is corrupted and data is either missing or invalid.
Any ideas?
I am using 3.5 if that helps..

Thanks