Пример кода прикрепленного к кнопке:
<script>
document.addEventListener('DOMContentLoaded', function () {
const formId = 'form2198503111';
const fileUrl = 'https://litlife.club/books/360921/files/Uolker_N._R.pdf.zip';
const fileName = 'Uolker_N_R.pdf.zip';

document.addEventListener('tildaform:aftersuccess', function (event) {
const form = event.target;

if (!form || form.id !== formId) return;

const link = document.createElement('a');
link.href = fileUrl;
link.download = fileName;
link.style.display = 'none';

document.body.appendChild(link);
link.click();
document.body.removeChild(link);
});
});
</script>