C# เขียน Download File PDF ทันทีหลังจากคลอกที่ปุ่มดาวน์โหลด

 Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click
        SaveFileDialog1.Filter = "Text Files (*.txt)|*.txt|All Files (*.*)|*.*"
        SaveFileDialog1.FilterIndex = 1
        If SaveFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
            Dim myStream As New StreamWriter(SaveFileDialog1.FileName, True)
            myStream.Write(RichTextBox1.Text)
            myStream.Close()
        End If
    End Sub

string path = "\\answer\\answer.pdf";
            SaveFileDialog sfd = new SaveFileDialog();
            sfd.FileName = Application.StartupPath + path;
            sfd.Filter = "PDF Files (*.PDF) | *.PDF| All Files|*.*";
            if (sfd.ShowDialog() == DialogResult.OK)
            {
                // Copy your file to sfd.FileName.
                System.IO.FileStream fs = (FileStream)sfd.OpenFile();
                //Console.WriteLine()
                string s = sfd.FileName;
                
            }