world-game/site/templates/white-paper.json.php

<?php

$specificData = [
    'published'  => $page->published()->toDate('d/m/Y'),
    'intro'      => $page->intro()->inline()->value(),
    'cover'      => $page->cover()->toFile()?->url(),
    'fileUrl'    => $page->downloadFile()->toFile()?->url(),
];

$pageData = array_merge($genericData, $specificData);

header('Content-Type: application/json');
echo json_encode($pageData);