You can generate, print, and save documents in Order Printer Pro in a couple of ways:
Printing a single order
In your Shopify admin
Go to the Orders section
Click on an order to open it
In the "More actions" dropdown, select Print with Order Printer Pro
Printing multiple orders at once
Shopify allows you to select up to 50 orders at once and then open apps with those orders selected.
In your Shopify Admin
Go to the Orders section
Put a checkmark on the orders you want to print for
In the actions bar, click on the three dots and select Print with Order Printer Pro
Note: You can select and print up to 50 orders at a time. The 50-order limit is something that Shopify controls, and apps cannot change that limit, unfortunately.