Hi, I would use a listbox on the left, and text widget on the right. The only glitch is that a left click on a listbox is predefined to select an item, so I made a right-click to actually open the file.

P.S. I see you want to draw figures on the right, so make it a canvas and do what you need to do.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = Tk::MainWindow->new( -title => 'Left-click -> select ... Righ
+t-click -> view' );

my $frame = $mw->Frame()->pack();

my @files =  get_sub_dirs('.');

my $lb = $frame->Scrolled('Listbox',
             -listvariable => \@files,
             -scrollbars => 'osoe', #only if needed
         )->pack(-side => 'left', -fill=>'y',-expand =>1);

my $text = $frame->Scrolled('Text',
             -scrollbars => 'osoe', #only if needed
         )->pack(-side => 'right');


$lb->bind( '<ButtonPress-3>', [ \&view_it, Ev('@') ] );

MainLoop;

sub view_it {
    my ( $lb, $xy ) = @_;

    $lb->selectionClear( 0, 'end' );
    my $index = $lb->index($xy);
    my $file;
    if ( defined($index) ) {
        $lb->selectionSet($index);
        $file = $lb->get($index);
        
    $text->delete('1.0','end'); #clear out old file
        my $buf;    
        open (FH,"< $file");
        read( FH, $buf, -s FH );
        close FH;

        $text->insert('end', $buf);    
    
    }
}

##################################################################
sub get_sub_dirs {
  my $dir = shift;
  opendir my $dh, $dir or die "Error: $!";
  my @files = grep !/^\.\.?$/, readdir $dh;
  closedir $dh;

  @files = grep ! -d, @files; 
  return @files;
}
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