Fatal error after upgrade trying to open PDF

Hi, I upgraded last night (18th July 2017) to latest version of PDF Invoices plugin, tried to open orders this morning to print off and start packing and just get this on a blank screen:

Fatal error: Call to undefined function WPO\WC\PDF_Invoices\Documents\mb_convert_encoding() in /home/electricalironmo/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/documents/abstract-wcpdf-order-document.php on line 523

Is there any way I can go back to the working version I was using yesterday just to get my invoices printed today, then upgrade once I’ve figured out what’s gone wrong?

Many thanks