Hi,
That plugin is sold here and has never been part of HikaShop itself:
www.hikashop.com/marketplace/product/18-plugin-pdf.html
So if you're using it, we assume that you already purchased it (and you did, I checked).
So you already have access to it. Go in the menu My account>My orders, click on your order C3U4N1F37 and there you'll have a download link for it. It's the same link you used the first time you downloaded it.
The fix is already included there. Now if you want to patch the code without updating the plugin, you can just change the line:
echo implode(', ', $this->order->order_shipping_method);
to:
echo implode(', ', $order->order_shipping_method);
Mohamed just wanted to give you a simpler answer for you to apply.