我在Chrome中加载了内容脚本。当我在google驱动器中打印docx时，Chrome会在新页面中打开该文件，该文件嵌入文件如下：
<embed width="100%" height="100%" name="plugin" id="plugin" src="https://doc-10-78-apps-viewer.googleusercontent.com/viewer/secure/pdf/ir7ttre15krrkcd49ssmvhgcd62pctgr/g7os4cqtfut2cmfmtp6cbjtg0h8mjvpo/1501677900000/drive/06250768728759024610/ACFrOgDlcxE7Uuy3abO4J9PRed248Bo9jg98MyEkYAWd__U3toMC_UmFuduTui1avT4riw0WkJ76SDJgVmnRCux35KP_KCojyy6Oude4B463MJeySVSryycvi6dd-38=" type="application/pdf" internalinstanceid="9" title="">
如何阅读文件内容？我尝试了document.getElementById('plugin').contentDocument或document.getElementById('plugin').contentWindow但它们都不存在。