title: PyPDF2 ignores content, gets watermark only
body: <p>I have thousands of PDF files like <a href="https://www.docdroid.net/UeDNhd8/decisao-10166720039201098.pdf" rel="nofollow noreferrer">this one</a>.</p>
  
  <p>I'm trying to use PyPDF2 to convert them to plain text (code is below). But PyPDF2 apparently only "sees" the watermarks, not the content itself. What could I do here?</p>
  
  <pre><code>import os
  import PyPDF2
  
  path_to_pdfs = '/path/to/pdf/files/'
  for filename in os.listdir(path_to_pdfs):
      if '.pdf' in filename.lower():
          with open(path_to_pdfs + filename, mode = 'rb') as f:
              txt = ''
              pdf_reader = PyPDF2.PdfFileReader(f)
              num_pages = pdf_reader.numPages
              for page in range(num_pages):
                  page_obj = pdf_reader.getPage(page)
                  page_text = page_obj.extractText()
                  txt = txt + '\n' + page_text
              print(txt)
  </code></pre>
  
  <p>I'm using Python 3.5.1 and PyPDF2 1.26.0 on macOS 10.13.14.</p>