Send attachment with Email using windows form application

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.NET

.NET4

In my winforms application,i created a winform to send EmailNow i want to attach a file(image,doc or other file) with this mail and send this file. How can i perform this?Code is here:

using System.Net;
using System.Net.Mail;

private void button1_Click(object sender, EventArgs e)
        {
             try
            {
                
                string idfrom = textBox1.Text;
                String password = textBox2.Text;
                String idto = textBox3.Text;
                string msg = richTextBox1 .Text ;
                string sub = textBox4.Text;
                var smtp = new SmtpClient();
                {
                    smtp.Host = "smtp.gmail.com";
                    smtp.Port = 587;
                    smtp.EnableSsl = true;
                    smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
                    smtp.Credentials = new NetworkCredential(idfrom,password);
                    smtp.Timeout = 20000;
                }
                smtp.Send(idfrom, idto, sub , msg);
                MessageBox.Show("Message has been sent");
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message );
            }        
        }

Thanks