private void corDePáginaToolStripMenuItem_Click(object sender, EventArgs e)
 {
     Cor_cdl.ShowDialog();
     pagina_rtb.BackColor = Cor_cdl.Color;
 }
 private void corDeFonteToolStripMenuItem_Click(object sender, EventArgs e)
 {
     Cor_cdl.ShowDialog();
     pagina_rtb.SelectionColor = Cor_cdl.Color;
 }