private void MdiAppointmentManagerForm_Load(object sender, EventArgs e)
        {
            AppointmentManagerForm form = new AppointmentManagerForm();

            form.MdiParent = this;
            form.Show();
        }
 private void OpenAppointmentForm()
 {
     using (var form = new AppointmentManagerForm())
     {
         form.MdiParent = this;
         form.Show();
     }
 }