title: Converting multiple .pdf files with multiple pages into 1 single .csv file
body: <p>I am trying to convert .pdf data to a spreadsheet. Based on some research, some guys recommended transforming it into csv first in order to avoid errors. </p>
  
  <p>So, I made the below coding which is giving me:
  <strong>"TypeError: cannot concatenate object of type ''; only Series and DataFrame objs are valid"</strong></p>
  
  <p>Error appears at 'pd.concat' command.</p>
  
  <p>'''</p>
  
  <pre><code>import tabula
  import pandas as pd
  import glob
  
  
  path = r'C:\Users\REC.AC'
  all_files = glob.glob(path + "/*.pdf")
  print (all_files)
  
  df = pd.concat(tabula.read_pdf(f1) for f1 in all_files)
  df.to_csv("output.csv", index = False)
  </code></pre>
  
  <p>'''</p>