I have a problem to attach official letter that have been create in the system which is in pdf to lecturer's email that have in the database.
public function approve($id,Request $request) {
    try {
        $letter = Letter::where('id',$id)
        ->update([
            'isApproved' => 1,
            'approvedBy' => $request->session()->get('users.id')
            ]);
        $letter = Letter::where('id',$id)
        ->first();
        $lecturer = User::where('id',$letter->user_id)
        ->get();
        $emailBody="Hello, ".$lecturer[0]->username.",<br>".
        "Your letter have been approved by ".$request->session()->get('users.username').".<br>".
        "Kindly check the attachment. Thank you.<br><br>".
        "This is system generated email. Please do-not reply on this email.";
        mail($lecturer[0]->email, "Certification Approved", $emailBody);
        return redirect()
        ->back()
        ->with('success_approve_letter','Record successfully approve');
    } catch (Exception $e) {
        return redirect()
        ->back()
        ->withErrors(["Error: ".$e->getMessage()]);
    }
}
But in the email, it just send this.