I suppose for small files, that you want to display readonly, and don't want the overhead of the full Text widget, a Label might be a good choice for display.

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

my $mw = Tk::MainWindow->new();

#open this script as an example
open(  my $fh,"< $0" ) or die "$!\n"; 
my $buf;
read( $fh, $buf, -s $fh );
close $fh;


my $lab1=$mw->Label(-text => 'abc abc abc abc abc abc abc abc abc abc 
+abc abc',
    -bg=>'white',
    -width => 40,
    -wraplength => 200,
    )->pack(-expand=> 0, -fill=> 'x');

my $lab2=$mw->Label(-text => 'abc abc abc abc abc abc abc abc abc abc 
+abc abc',
    -bg=>'lightblue',
    -width => 40,
    -wraplength => 100,
    )->pack(-expand=> 0, -fill=> 'x');


my $lab3=$mw->Label(-text => $buf,
    -bg=>'hotpink',
    -width => 40,
    -wraplength => 200,
    -justify => 'left',
    -anchor  => 'w',
    )->pack(-expand=> 0, -fill=> 'x');

MainLoop;
[download]

You don't want to do that, you want to use a Text widget

You can see several examples if you run the Tk demonstration program "widget", or see the program "gedi"

While you're at it, you might as well read Tk Tutorial