The example below uses the CAM::PDF module, which you use here and I suspect this post relates to.

#!/usr/bin/perl
use strict;
use warnings;
use CAM::PDF;

my $pdf = CAM::PDF->new('test.pdf');
my $pagecontent = $pdf->getPageContent(1);

# $pagecontent now holds the text within the first page.
# say I want to replace the word Release with Distribution.

$pagecontent =~ s/Release/Distribution/;

$pdf->setPageContent(1, $pagecontent);
$pdf->cleanoutput('test_replace.pdf');
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If you have any interest in learning Perl I suggest you take the time to read:

• perlintro
• http://learn.perl.org
• http://perldoc.perl.org
• Browse the Tutorials section of this site.