Custom em_printables_pdf_get_invoice_number filename

<?php

function filename( $filename, $EM_Booking ){

	$filename = $EM_Booking->output( get_option( 'dbem_bookings_pdf_invoice_format' ) );

	return $filename;
}
add_filter('em_printables_pdf_get_invoice_number', 'filename', 100, 2 );