title: Validate FileField django as a valid pdf
body: <p>I'm new to django and I hope you can  guide me with this, I have a model definition like this: </p>
  
  <pre><code>class Documents(models.Model): 
      name = models.CharField(max_length=255)
      date = models.DateField()
      path = models.FileField(upload_to='documents/')
  </code></pre>
  
  <p>But I need to validate it as a valid PDF file, could you guide me how to do that? </p>