Navigation Drawer not visible

Question

I am working on an app right now, the main component is to display pdf's. I have used the plugpdf library for this, with this code in the mainactivity:

try{
    // Initialize PlugPDF with a license key.
    PlugPDF.init(getApplicationContext(),
            "my license key here, censored for obvious reasons");
} catch (PlugPDFException.InvalidLicense ex) {
    Log.e("PlugPDF", "error ", ex);
    // Handle invalid license exceptions.
}


SimpleDocumentReader v = SimpleReaderFactory.createSimpleViewer(this, null);
v.openUrl(link, "123456");

So basically, I am opening an activity in the mainactivity. Here's how it looks like.

The problem with this is, that the simpledocumentreader (the activity for the pdf viewer), is "on top" of the main activity, that means, if I click on the Navigation Drawer icon, I won't see anything.

Here's how it is supposed to look like. (The pdf should be still visible in the background)

So, basically I somehow need to achieve putting the navigation drawer "on top" of the SimpleDocumentReader. Strangely, I create the pdf reader view first, and then the navigation drawer fragment, and still, the pdf appears on top of the navigation drawer. So, the question is, how?