how can we send attached file with notification in gmail in laravel 8 code example

Example: how can we send attached file with notification in gmail in laravel 8

public function toMail($notifiable)
    {
        return (new MailMessage)
                    ->line('Please download the PDF.')
                    ->attach(public_path($this->filename), [
                        'as' => 'filename.pdf',
                        'mime' => 'text/pdf',
                    ]);
    }