private void MainForm_Load(object sender, EventArgs e)
        {
            CustomerForm customerForm = new CustomerForm();

            customerForm.Dock      = DockStyle.Right;
            customerForm.MdiParent = this;
            customerForm.TopLevel  = false;
            customerForm.Closed   += CustomerForm_Closed;
            customerMenu.Enabled   = false;
            customerForm.Show();
        }
        private void CustomerMenu_Click(object sender, EventArgs e)
        {
            CustomerForm customerForm = new CustomerForm();

            if (Application.OpenForms.OfType <ProfileForm>().FirstOrDefault() != null)
            {
                customerForm.EnableButtons(false);
            }

            customerForm.Dock      = DockStyle.Right;
            customerForm.MdiParent = this;
            customerForm.TopLevel  = false;
            customerForm.Closed   += CustomerForm_Closed;
            EnableCustomerMenu(false);
            customerForm.Show();
        }