#!/usr/bin/perl -w

$file = $ARGV[0];
open(FILE, "file '$file' |");
$line = <FILE>;
close(FILE);
unless($line =~ /PDF document/) {
  print "Not converting $file\n";
  exit(0);
}

print "Converting $file\n";
((system("pdftotext '$file' - > /tmp/CONV.$$") / 256) == 0) or 
  die "System failed.";
system("mv /tmp/CONV.$$ '$file'");