How to disable the PDF viewer in X7

In most cases, I read the information of one literature first, and decide I have to read the PDF or not. But the viewer always opens the PDF and makes Endnote much slower. I think this is not good.

Either turn off the reference panel in Layout, or make sure it is selected on the reference or preview tab, not pdf tab?  I rarely use the viewer.  I open the pdf in adobe.  

To disable the tab is enough. The tab always opens PDF file without my permission which wastes the system resource and makes the software slow, I can use Adobe Reader to read PDF when I want to read it.