malajner

Thank for reply. I solved issue a little bit different. Just added meta container on admin shop order page which open default email client and generate new message with subject, address an order number. And then I manually send the mail.

// Adding Meta container admin shop_order pages
add_action( 'add_meta_boxes', 'mv_add_meta_boxes' );
if ( ! function_exists( 'mv_add_meta_boxes' ) )
{
    function mv_add_meta_boxes()
    {
        add_meta_box( 'mv_other_fields', __('Pripravi email sporočilo za pošiljanje pdf računa','woocommerce'), 'mv_add_other_fields_for_packaging', 'shop_order', 'side', 'core' );
    }
}

// Adding Meta field in the meta container admin shop_order pages
if ( ! function_exists( 'mv_add_other_fields_for_packaging' ) )
{
    function mv_add_other_fields_for_packaging($order_id)
    {
        global $post;

        $meta_field_data = get_post_meta( $post->ID, '_my_field_slug', true ) ? get_post_meta( $post->ID, '_my_field_slug', true ) : '';
		$order = wc_get_order( $order_id );
		$order->get_id();
		$narocilo =$order->get_id();
		$email =$order->get_billing_email();
		//$current = WC()->cart->subtotal;
		

		?>
			<form>
			<input class="button" value="Pripravi email" onclick="window.location.href='mailto:<?php echo $email ?>?subject=Račun za naročilo: <?php echo $narocilo ?> - Markla&body=Spoštovani, v prilogi vam pošiljamo račun za naročilo št.: <?php echo $narocilo ?>.'" />
			</form>
		<p>Pošlji na naslov: <?php echo $email ?></p>
    <?php

       
    }
}