PDF Invoice Number instead of standard WordPress Order Number

Forgot to mention, in another topic I saw it the other way around. I would like to do the opposite, using the invoice number as order number:

/**
 * Format order number with invoice number settings
 */
add_filter( 'wpo_wcpdf_invoice_number', 'wpo_wcpdf_format_invoice_number', 20, 4 );
function wpo_wcpdf_format_invoice_number( $invoice_number, $order_number, $order_id, $order_date ) {
	// We want to use the order number as invoice number!
	$invoice_number = ltrim($order_number, '#');

	// get format settings
	$template_settings = get_option('wpo_wcpdf_template_settings');

	$formats['prefix'] = isset($template_settings['invoice_number_formatting_prefix'])?$template_settings['invoice_number_formatting_prefix']:'';
	$formats['suffix'] = isset($template_settings['invoice_number_formatting_suffix'])?$template_settings['invoice_number_formatting_suffix']:'';
	$formats['padding'] = isset($template_settings['invoice_number_formatting_padding'])?$template_settings['invoice_number_formatting_padding']:'';

	// Replacements
	$order_year = date_i18n( 'Y', strtotime( $order_date ) );
	$order_month = date_i18n( 'm', strtotime( $order_date ) );

	foreach ($formats as $key => $value) {
		$value = str_replace('[order_year]', $order_year, $value);
		$value = str_replace('[order_month]', $order_month, $value);
		$formats[$key] = $value;
	}

	// Padding - minimum of 3 for safety
	if ( ctype_digit( (string)$formats['padding'] ) && $formats['padding'] > 3 ) {
		$invoice_number = sprintf('%0'.$formats['padding'].'d', $invoice_number);
	}

	$formatted_invoice_number = $formats['prefix'] . $invoice_number . $formats['suffix'] ;

	return $formatted_invoice_number;
}

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