get uploaded file, accept only PDF extension, give random file name and store to folder

if(isset($_FILES['file'])){
  $errors = array();
  $file_name = $_FILES['file']['name'];
  $file_size = $_FILES['file']['size'];
  $file_tmp = $_FILES['file']['tmp_name'];
  $file_type = $_FILES['file']['type'];
  $file_ext = strtolower(end(explode('.', $_FILES['file']['name'])));
  $extensions = array("pdf");

  if(in_array($file_ext, $extensions) === false){
    $errors[] = "extension not allowed, please choose a pdf file.";
  }

  if($file_size > 2097152) {
    $errors[] = 'File size must be excately 2 MB';
  }

  if(empty($errors) == true) {
    move_uploaded_file($file_tmp, "files/".$file_name);
    echo "Success";