code: public void addFile(File file) throws HelloSignException {
          if (!(request instanceof SignatureRequest)) {
              throw new HelloSignException("Cannot add files to this unclaimed draft");
          }
          ((SignatureRequest) request).addFile(file);
      }
docs: Adds a file to the unclaimed draft.
  
  @param file File
  @throws HelloSignException thrown if there is a problem adding the File.