Function app.openDoc not returning Doc object although run in privileged function

Hello, 

I would very much appreciante your help. I have a privileged function stored on my local PC:

global.trustedSimpleFcn = app.trustedFunction(function(originalDoc) 
{

	app.beginPriv();
	var originalPath = originalDoc.path;

	// Get the path for the temp file
	var tempPath = app.getPath("user", "temp") + "/esc_temp_pdf.pdf";

	// This saves the original file as temp
	originalDoc.saveAs(tempPath);

	// Open original again
	app.openDoc(originalPath); 

	// Open the temp to get the doc object
	this.disclosed = true; // Because I heard it must be disclosed ??
	app.openDoc(originalPath); 
	var tempDoc = app.openDoc(tempPath);
	if (!tempDoc) {
	app.alert("tempDoc is empty!", 0, 0, "Error");
	app.endPriv();
	return "";
	}

	app.endPriv();
	app.alert("tempDoc is provided!", 0, 0, "Info");
	return tempDoc.documentFileName;
})

I am basically trying to save a copy of the current document as temp (and later manipulate it, flatten form and move it as a first page to other document, like a document header). For that I need to open a document and get the document object 'tempDoc' to be able to work with it.

I call this privileged function in button like this:

console.println(global.trustedSimpleFcn(this));

and tempDoc is empty. However if I run this one line of code in console, the tempDoc is provided ALTHOUGH this is run inside the privileged function. Why is there a difference? How can I fix it?

Regards,

Filip