Creating a document template within a custom module

Ciao,
my custom module must contain the templates of some documents (invoices, orders, …).
Following the wiki, I derived my class from an existing one (eg crabe for the invoice), saving my php in the same folder I started from, and the new template appears in the list and can be used correctly.

But I don’t understand how to move the file inside my custom module folder (e.g. custom / mymodule / core / modules / doc).
How can I do?

Thank you