Use Time::Piece to handle the date conversion. The following program works for files specified on the command line without path, so you have to cd to the containing directory before running it.

#! /usr/bin/perl
use warnings;
use strict;

use Time::Piece;

for my $file (@ARGV) {
    open my $IN, '<', $file or do {
        warn "Can't open '$file', skipping.\n";
        next
    };
    <$IN>;                                           # Skip the first 
+line.
    my $date_string = <$IN>;
    chomp $date_string;                              # Remove newline.
    my $date = 'Time::Piece'->strptime($date_string, '%B %d, %Y');
    rename $file, $date->ymd(q()) . "-$file" or warn "Can't rename $fi
+le\n";
}
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