use Crypt::OpenPGP;
use File::Slurp;

my $pgp = Crypt::OpenPGP->new(Compat => 'GnuPG');
my $phrase=read_file('file.txt');

my ($plaintext,$valid,$sig)=$pgp->decrypt(
    Data => $phrase,
    Passphrase => "abc123!",
);
print "[message: $plaintext<br>valid: $valid<br>signature: $sig<br>error: ".$pgp->errstr."]<br><br>\n";