(untested)

#!/usr/bin/perl

use strict;
use warnings;
use Proc::ProcessTable;

my $p=Proc::ProcessTable->new;
my $wanted=1234;

for ( @{$p->table} ) {
    print "Found\n" and last if $_->pid == $wanted;
}

__END__
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To get access to the pid I would use $process->pid.

No, you would use the pid() method on the objects of $process->table() which are instances of the class Proc::ProcessTable::Process.