getPath

Hi, I'm trying to get a path string from an open document but not sure how to code it.
 
I know that I need
app.execMenuItem("Open");
to have the user go and choose the file.
 
I know I need
getPath
to get a path string
 
So the why I was doing this is not working can someone help me here.
 
var t = app.execMenuItem("Open");
 
var mypath=app.getPath({I don't understand this part here});
 
And Then I would like it to go in my insertPages
 
this.insertPages({nPage: -1, cPath: mypath,});
 
Or there a better way of doing this?