code: public File getTemplateFile(String templateId) throws HelloSignException {
          String url = BASE_URI + TEMPLATE_FILE_URI + "/" + templateId;
          String fileName = TEMPLATE_FILE_NAME + "." + TEMPLATE_FILE_EXT;
          return httpClient.withAuth(auth).get(url).asFile(fileName);
      }
docs: Retrieves the PDF file backing the Template specified by the provided
  Template ID.
  
  @param templateId String Template ID
  @return File PDF file object
  @throws HelloSignException thrown if there's a problem processing the
  HTTP request or the JSON response.