如何在单独的窗口中打开的selenium webdriver中保存pdf？

Question

<input type="button" name="common.image.alt.print" value="Print   
  onclick="window.open('/ftol/pdf/RenderForm.do?   
formId=23907&formType=DEP_RECEIPT_RSP');clickPrint(0)" class="btnFont floatLeft" id="btn_0" alt="Print" />