Spring MVC populate PDF in popup window

I have issue to populate PDF in popup window using Spring MVC. I have two windows to work with. One is parent window and the other one is popup window initialed by the parent window/page. The PDF only populates to parent window but not popup.

My scenario is when clicking the button from the parent page and it opens a new popup window and showing the status. Once the PDF finished generating, it should display in popup window. But the PDF displays in parent window instead.

How can I set in the controller and let the PDF display in popup window? Please help.

Thanks.