WooCommerce ESR-Code Integration

General information for the website: We sell engraveable products
Kind of development: Customization of existing website
Description of requirements/features: Dear Developers

In Switzerland, for bill payments, there is a form with a code, which is used for processing the payments on banks. It's called ESR and consists of the account number, the order total and a check digit, which is calculated with Modulo 10.

It's not necessary to develop the calculation, as this is already available as free downloadable php code:
http://sprain.ch/blog/class-esr-besr-einzahlungsschein-php/

This page describes pretty well, how it could be implemented with PHP. I need a developer, who can integrate this to my woocommerce store and link it to the JetPack PDF-invoice.
The development consists of creating new fields for the calculated ESR codes (two codes), which should be visible in the orders backend, and the PDF output of it (which is also described in the link). We currently already have a PDF invoice provided by a plugin for PDF invoices. It would be great, to add this ESR form as a second page to the already existing PDF-invoice of that plugin.

This should be integrated as a plugin, so that it doesn't break on updates.

I need a developer, who has time to work on this as soon as possible.

Many thanks for your proposals and best regards
Tolga