test.js

window.addEventListener("documentViewerLoaded", function () {
	TXDocumentViewer.signatures.setSubmitCallback(signatureComplete);
});

function signatureComplete(e) {
    var element = document.createElement('a');
    element.setAttribute('href','data:application/pdf;;base64,' + e);
    element.setAttribute('download', "results.pdf");
    document.body.appendChild(element);
    element.click();
}