code: public byte[] getDocumentPageImage(String accountId, String envelopeId, String documentId, String pageNumber) throws ApiException {
      return getDocumentPageImage(accountId, envelopeId, documentId, pageNumber, null);
    }
docs: Gets a page image from an envelope for display.
  Retrieves a page image for display from the specified envelope.
  @param accountId The external account number (int) or account ID Guid. (required)
  @param envelopeId The envelopeId Guid of the envelope being accessed. (required)
  @param documentId The ID of the document being accessed. (required)
  @param pageNumber The page number being accessed. (required)
  @return byte[]