$ cat foo.pl
#!/usr/bin/perl
use strict;
use warnings;

my $dir = '.';
my $cat = '/bin/cat';
opendir DIR, $dir or die "Cannot open directory $dir:$!\n";
my @pdb_files = grep { -f $_ && $_ =~ /\.pdb$/ } readdir DIR;
closedir DIR;

for my $file (@pdb_files) {
    my $content = `$cat "$dir/$file"`;
    chomp $content;
    print "Content of $file is $content\n";

}