use CAM::PDF;

my $pdf = CAM::PDF->new('Test1.pdf');  # existing document
my $page = $pdf->getPageContent(1);

# $page now holds the uncompressed page content as a string

# replace the text part
$page =~ s/some placeholder text/my new text/;

$pdf->setPageContent(1, $page);
$pdf->cleanoutput('Test2.pdf');