/**
     * Get the mail representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return \Illuminate\Notifications\Messages\MailMessage
     */
    public function toMail($notifiable)
    {
        return (new MailMessage)
                    ->line('Please download the PDF.')
                    ->attach(public_path($this->filename), [
                        'as' => 'filename.pdf',
                        'mime' => 'text/pdf',
                    ]);
    }