Code:
private void button1_Click ( object sender, EventArgs e )
{
Graphics g = this.richTextBox1.CreateGraphics ();
Pen p = new Pen ( System.Drawing.Color.Black, 8 );
g.DrawLine ( p, 0, 10, this.Width, 10 );
this.richTextBox1.SendToBack ();
}
private void button1_Click ( object sender, EventArgs e )
{
Graphics g = this.richTextBox1.CreateGraphics ();
Pen p = new Pen ( System.Drawing.Color.Black, 8 );
g.DrawLine ( p, 0, 10, this.Width, 10 );
this.richTextBox1.SendToBack ();
}