Hi,

If you need to adjust content of your pdf based on the record data, you have to design a report in odoo in needed format using the studio or from custom module.

If just need to print a common PDF always, you can add a button and return the static PDF stored in your module or you can add some options in the user interface to store this data, in sale settings or as per your need.

Easy solution:
* add it as attachment in the db, from attachment menu
* make it public and get the url of attachment from local_url variable in the attachment model
* add a button in sales, redirect to this url on clicking the button

Thanks