The order status page is the final page of your store's checkout. The order status page lets your customers view their order details, status and tracking information online at anytime.
You can also add the PDF link to the Order Status page, allowing customers to download the document by clicking a button.
Navigate to the checkout page of your Shopify admin:
Scroll down to the section titled "Order processing" and find the field named "Additional scripts"
Paste the code provided to you in the Order Printer Emailer into the "Additional scripts" field.
Click "Save" and you are done!