Here's my method for generating quotation_order pdf's with Java if anyone finds this in the future:

private void generateOrderReport(final Object internalOdooQuoteId) throws XmlRpcException, IOException {
    logger.info("generating quote report pdf for order #: " + internalOdooQuoteId);
    final Object internalOdooQuoteIds = asList((Object[]) models.execute("execute_kw", asList(
      db, uid, password,
      "sale.order", "search",
      asList(asList(
        asList("id", "=", internalOdooQuoteId)
      )),
      new HashMap() {{
        put("limit", 1);
      }}
    )));
    final XmlRpcClientConfigImpl report_config = new XmlRpcClientConfigImpl();
    report_config.setServerURL(
      new URL(String.format("%s/xmlrpc/2/report", url)));
    final Map<String, Object> result = (Map<String, Object>)models.execute(
      report_config, "render_report", asList(
        db, uid, password,
        "sale.report_saleorder",
        internalOdooQuoteIds));
    final byte[] report_data = DatatypeConverter.parseBase64Binary(
      (String)result.get("result"));
    File file = new File("records/quotation_order.pdf");
    FileUtils.writeByteArrayToFile(file, report_data);
  }