Welcome! If it "doesn't run" does it throw an error? Try:

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

my $file_name="test.pdf";
my $pdf = CAM::PDF->new($file_name); 
my $pageone_tree = $pdf->getPageContentTree(1); # replaced 4 with 1 fo
+r testing 
$pageone_tree->render("CAM::PDF::Renderer::Dump");
[download]

Note the last line, it's directly taken from the CAM::PDF::Renderer::Dump documentation. This prints the coordinates of each node of a page layout, your post suggests you want to read the content, investigate the other methods this module offers such as getPageContent. See also PerlMonks for the Absolute Beginner.

Update: removed typo from last sentence.