title: Why I can't import pdfplumber
body: <p>When I was trying to import pdfplumber, it gives me error.</p>
  
  <p>Python 3.6.5 |Anaconda, Inc.| (default, Apr 26 2018, 08:42:37) 
  Type 'copyright', 'credits' or 'license' for more information
  IPython 6.4.0 -- An enhanced Interactive Python. Type '?' for help.</p>
  
  <h2>In [1]: import pdfplumber</h2>
  
  <p>ImportError                               Traceback (most recent call last)
   in ()
  ----> 1 import pdfplumber</p>
  
  <p>/anaconda3/lib/python3.6/site-packages/pdfplumber/<strong>init</strong>.py in ()
  ----> </p>
  
  <pre><code>1 from pdfplumber.pdf import PDF
        2 import pdfplumber.utils
        3 import pdfminer
        4 import pdfminer.pdftypes
        5 from ._version import __version__
  </code></pre>
  
  <p>/anaconda3/lib/python3.6/site-packages/pdfplumber/pdf.py in ()
        4 </p>
  
  <pre><code>    5 from pdfminer.pdfparser import PDFParser
  ----&gt; 6 from pdfminer.pdfdocument import PDFDocument
        7 from pdfminer.pdfpage import PDFPage
        8 from pdfminer.pdfinterp import PDFResourceManager,
  </code></pre>
  
  <p>PDFPageInterpreter</p>
  
  <p>/anaconda3/lib/python3.6/site-packages/pdfminer/pdfdocument.py in ()</p>
  
  <pre><code>    24 from .pdftypes import PDFTypeError
       25 from .pdftypes import PDFStream
  ---&gt; 26 from .pdftypes import PDFObjectNotFound
       27 from .pdftypes import decipher_all
       28 from .pdftypes import int_value
  </code></pre>
  
  <p>ImportError: cannot import name 'PDFObjectNotFound'</p>
  
  <p>Any solutions? </p>
  
  <p>Thanks!</p>