The following code allows a number of top level windows to be opened by clicking a button in the main window. A little work will get OP to creating a Text widget in each window to display the text files.

use strict;
use warnings;
use Tk;

my $main = MainWindow->new;
$main->Button (-text => "new window", -command => \&newTextWnd)->pack 
+();
MainLoop;

sub newTextWnd
{
$main->Toplevel ();
}
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