there are a bunch of action hooks in the order page (wppizza-order.php) , thank you page (wppizza-show-order.php) and order history page (wppizza-orderhistory.php) starting with

do_action('some_action',$some_variable(s)) 

for example, if you would like to add a print button at the top of the thank you page, you could add the following to your theme’s function.php

add_action('wppizza_show_order_before','my_print_button');
function my_print_button($cart){
print"<input type='button' value='print' onclick='window.print();return false;' />";
}