#!/bin/perl -w
use strict;

my $last_line='';

while( <DATA>)
  { chomp;
    if( m{\bedit\b})
      { # edit to taste
        $last_line .= ' # edited';
      }
    print $last_line, "\n"; 
    $last_line= $_;         # buffer the line
  }
print $last_line, "\n";

__DATA__
***********************
word1  word2
word4  word3
word4  word5  word6
word7  word8  word9 edit
word10 word11
word12 word13 edit
************************