code: public File getFinalCopy(String requestId) throws HelloSignException {
          String url = BASE_URI + SIGNATURE_REQUEST_FINAL_COPY_URI + "/" + requestId;
          String filename = FINAL_COPY_FILE_NAME + "." + FINAL_COPY_FILE_EXT;
          return httpClient.withAuth(auth).get(url).asFile(filename);
      }
docs: Retrieves the final PDF copy of a signature request, if it exists.
  
  @param requestId String SignatureRequest ID
  @return File final copy file, or null if it does not yet exist
  @throws HelloSignException thrown if there's a problem processing the
  HTTP request or the JSON response.
  @deprecated Use {{@link #getFiles(String)}