example_2_guesser.php

<?php
use Symfony\Component\Mime\{MimeTypes, FileBinaryMimeTypeGuesser};

class FileCreator
{
  public function create(string $filePath): void
  {
    $mimeTypes = new MimeTypes();
    
    // The last registered guesser has precedence over the other ones.
    $mimesTypes->registerGuesser(new FileBinaryMimeTypeGuesser);
    $mimeType = $mimeTypes->guessMimeType($filePath);
    
    if (false === $this->supports($mimeType)) {
      // throw error
    }
    // stuff
  }
  
  private function supports(?string $mimeType): bool
  {
     return 'application/pdf' === $mimeType;
  }
}