add_submenu_page(
        'smart-crm',
        __('WP SMART CRM Documents', 'mytextdomain'),
        __('Documents', 'mytextdomain'),
        'manage_options',
        admin_url('admin.php?page=smart-crm&p=documenti/list.php'),
        ''
        );

$adminurl=admin_url();
add_submenu_page(
    'smart-crm',
    __('WP SMART CRM Documents', 'mytextdomain'),
    __('Documents', 'mytextdomain'),
    'manage_options',
    $$adminurl.'admin.php?page=smart-crm&p=documenti/list.php',
    ''
    );

add_submenu_page(
    'smart-crm',
    __('WP SMART CRM Documents', 'mytextdomain'),
    __('Documents', 'mytextdomain'),
    'manage_options',
    'admin.php?page=smart-crm&p=documenti/list.php',
    '');