title: PDF Miner PDFEncryptionError
body: <p>I'm trying to extract text from pdf-files and later try to identify the references. I'm using pdfminer 20140328. With unencrypted files its running well, but I got now a file where i get:</p>
  <blockquote>
  <p>File &quot;C:\Tools\Python27\lib\site-packages\pdfminer\pdfdocument.py&quot;, line 348, in _initialize_password</p>
  <p>raise PDFEncryptionError('Unknown algorithm: param=%r' % param)</p>
  <p>pdfminer.pdfdocument.PDFEncryptionError: Unknown algorithm: param={'CF': {'StdCF': {'Length': 16, 'CFM': /AESV2, 'AuthEvent': /DocOpen}}, 'O': '}\xe2&gt;\xf1\xf6\xc6\x8f\xab\x1f&quot;O\x9bfc\xcd\x15\xe09~2\xc9\\x87\x03\xaf\x17f&gt;\x13\t^K\x99', 'Filter': /Standard, 'P': -1548, 'Length': 128, 'R': 4, 'U': 'Kk&gt;\x14\xf7\xac\xe6\x97\xb35\xaby!\x04|\x18(\xbfN^Nu\x8aAd\x00NV\xff\xfa\x01\x08', 'V': 4, 'StmF': /StdCF, 'StrF': /StdCF}</p>
  </blockquote>
  <p>I checked with pdfinfo, that this file seemed to be AES encrypted, but i can open it without any problems.
  So i have two questions:</p>
  <ul>
  <li><p>at first: how is it possible that a document is encrypted but i can open it without a password?</p>
  </li>
  <li><p>and secondly: how do i make PDFMiner read that file properly? Somewhere i read to install pycrypto to get additional algorithms but it doesnt fixed my problem.</p>
  </li>
  </ul>
  <p>Many thanks.</p>