PHP密码保护表单帮助.1输出工作，倍数不

我想弄清楚为什么一种形式的工作，但我的另一个没有。我试图创建一个表单，让用户选择各种包，输入密码，然后有能力下载说的文件，如果它是正确的。我可以在一个文件中这样做

<?php
 // Get the password
      $pw = md5($_POST['password']);
 // Compare against the stored password
      $valid_pw = md5("example");
      if($pw != $valid_pw){
           echo "Error! You do not have access to this file";
      }else{
           header("Location:files'bundle1.pdf");
      }
?>

然而，我不能让这个工作。当我做出选择，输入密码并点击提交时，我看到一个空白屏幕，URL是PHP文件。下面是代码:

<?php
 // Get the password
        $pw = md5($_POST['password']);                    
        $bundle1 = ($_POST['1']);
        $bundle2 = ($_POST['2']);
        $bundle3 = ($_POST['3']);
        $bundle4 = ($_POST['4']);
 // Compare against the stored password
      $valid_pw = md5("example");
      if($pw != $valid_pw){
           echo "Error! You do not have access to this file";
      }else{
$bundle1 = 'unchecked';
$bundle2 = 'unchecked';
$bundle3 = 'unchecked';
$bundle4 = 'unchecked';
if (isset($_POST['download'])) {
     $selected_radio = $_POST['bundle'];
     if ($selected_radio == '1') {
            $bundle1 = 'checked';
            header("Location:files'bundle1.zip");
            exit();
      }else if ($selected_radio == '2') {
            $bundle2 = 'checked';
            header("Location:files'bundle2.zip");
            exit(); //added exits so program wouldn't continue to run after selection -k
      }
      else if ($selected_radio == '3') {
            $bundle3 = 'checked';
            header("Location:files'bundle3.zip");
            exit();
      }
      else if ($selected_radio == '4') {
            $bundle4 = 'checked';
            header("Location:files'bundle4.zip");
            exit();
      }
    }
 }
?>

主要区别(除了else if语句)是工作文件是。pdf，而非工作文件是。zip。这有什么区别吗?