magento2 – How to create extra PDF credit memo?

I need to create a custom module to add an extra PDF to credit memo. The idea is to have and extra button near “Print” button, called “Print custom PDF” in the credit memo admin interface and when I click on it to export a custom PDF. It can be created via file because it is used only for internal usage.

What I actually need is to have 2 PDF for credit memos, one for customers and one for admin with different layout and data.

How can I do this?