Document (PDF, TXT, DOCX) to text classes
You have two methods getText() and handle() of which one is not needed. Doing the conversion and returning the result should be one method. So, like this:

class Converter
{
    protected $file;
    protected $text;

    public function __construct($file)
    {
        $this-&gt;file = $file;
    }
}


and:

class PDFConverter extends Converter implements IConverter
{
    public function getPlainText()
    {
      if (is_null($this-&gt;text)) // not yet converted?
      {   
        $this-&gt;text = 'Text PDF'; // do the conversion
      }
      return $this-&gt;text; // return result
    }
}


This way you still buffer the result, but you get rid of the rather weird handle() method.

When using this class you don't have to think about the order in which to call the methods anymore, just ask for the plain version of the text and the method will do the conversion only once.

You might want to move the declaration of the $text field to the other class.