test.js

TXDocumentViewer.setSubmitCallback(saveSignedDocument);

function saveSignedDocument(e) {

    var serviceURL = "@Url.Action("SaveSignedDocument", "TX")";

    // send document to controller
    $.ajax({
        type: "POST",
        url: serviceURL,
        data: {
            document: e.document
        },
        success: successFunc,
        error: errorFunc
    });
    
    function successFunc(data, status) {
      alert("Thanks");
    }

    function errorFunc(data, status) {
      console.log(data);
    }
}