test.ts

async saveDocument() {

  var documentValidated = TXDocumentViewer.forms.validate();

  if (!documentValidated) {
    alert('Document is not valid!');
    return;
  }

  const saveSettings = { mergeFormFields: true, embedAnnotations: false };
  const result = await TXDocumentViewer.saveDocument(
    TXDocumentViewer.StreamType.InternalUnicodeFormat,
    saveSettings);

  const base64 = await result.base64();

  console.log(base64);

  this.http.post('/document/saveDocument', { document: base64, name: this.documentData.name }).subscribe(
    (result) => {
      console.log(result);
    }
  );
}