private void radRibbonBarGroup1_Click(object sender, EventArgs e)
 {
     Invoice inv = new Invoice();
     inv.MdiParent = this;
     inv.Show();
 }
 private void pictureBox5_Click(object sender, EventArgs e)
 {
     // toolStripProgressBar1.Maximum = max;
     // timer1.Start();
     //   timer1.Enabled = true;
     if (Application.OpenForms["Billing"] != null)
     {
         MessageBox.Show("Please close the Billing interface!", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information);
     }
     else if (Application.OpenForms["Invoice"] == null)
     {
         Invoice inv = new Invoice();
         inv.MdiParent = this;
         inv.Size = new System.Drawing.Size(1100, 690);
         inv.Location = new System.Drawing.Point(5, 5);
         inv.Show();
     }
 }