test.ts

async mergeDocument() {

  // get the saved document from TXTextControl
  let postDocument: MergedDocument = {
    document: await saveDocument(),
  };

  // post the document to endpoint 'MergeDocument'
  this._http.post<MergedDocument>(this._baseUrl + 
    'textcontrol/mergedocument', postDocument).subscribe(result => {

    // load the results into TXDocumentViewer
    loadDocumentViewer(result.document);

  }, error => console.error(error));

}

function loadDocument(Document) {
  TXDocumentViewer.loadDocument(Document.documentData, Document.documentName);
}