Hi! What you describe sounds more of a Local Pickup/WooCommerce issue than an issue with the PDF Invoices & Packing Slips plugin.

You can use any of the regular filters and actions in the PDF and query the order data to see if the shipping method is local pickup:

$shipping_method = $order->get_shipping_method();

You can change the shipping title on the invoice with wpo_wcpdf_shipping_method, here’s an example (you’ll need to change the shipping method title to the one used by Local pickup for this to work):

add_filter('wpo_wcpdf_shipping_method','wpo_wcpdf_shipping_method_pickup',10, 2);
function wpo_wcpdf_shipping_method_pickup( $shipping_method, $document ) {
	if ( $shipping_method == "Pickup" ) {
		$shipping_method = "NEW TITLE";
	}
	return $shipping_method;
}

Hope that helps!
Ewout

Is it possible to change it dynamically?

Technically, yes, you could use the gettext filter. But you’re entering hacky territory here 🙂

Without warranty:

add_action('wpo_wcpdf_before_html','wpo_wcpdf_dynamic_shipping_address_title',10,2);
function wpo_wcpdf_dynamic_shipping_address_title( $document_type, $document ) {
	if (!empty($document->order)) {
		$shipping_method = $document->order->get_shipping_method();
		if ( $shipping_method == "Pickup" ) {
			add_filter('gettext', function( $translation, $text, $domain ) {
			    if ( $domain == 'woocommerce-pdf-invoices-packing-slips' && ( $text == 'Ship To:' || $text == 'Shipping Address:' ) ) {
			        $translation = $translation = 'Recipient:';
			    }
			    return $translation;
			}, 10, 3 );
		}
	}
}

(as with the previous filter, change Pickup for the shipping method you want to address)

Very glad to hear that works for you 🙂

What I meant is that overriding translations programmatically is not very transparent and this method is not quite transparent even though it does exactly what you need right now.
It’s not necessarily unsafe but it’s certainly more ‘readable’ (for others or for yourself in say a year from now) to do this in the template. The choice is up to you.