test.ts

mergeTemplate() {

  TXTextControl.saveDocument(TXTextControl.StreamType.InternalUnicodeFormat, (document: any) => {

    this.mailMergeData.template = document.data;

    // send a post request to the server
    this.http.post('/mailmerge/mergetemplate', this.mailMergeData).subscribe(
      (result) => {
        this.mailMergeData = result;
        TXTextControl.loadDocument(
          TXTextControl.StreamType.InternalUnicodeFormat,
          this.mailMergeData.document);
      }
    );

  });
}