If your Shopify store is selling in multiple currencies using the Shopify multi-currency feature or Shopify Markets' local currencies, Order Printer Pro will automatically display all amounts using the customers' currency.
No changes are needed to the templates; they will automatically detect which currency the customer used and display the amounts correctly.
Note: For draft orders, you'll see the store currency instead of the customer's because Shopify simply do not provide the same information related to the other currency prices that they do for regular orders.
If you are using a third-party app to add multi-currency to your store, it is not possible to display amounts in the order currency. They, unfortunately, do not add enough information to orders to make this possible.