Check whether a PDF file is valid with Python

If you’re on a Linux or OS X box, you could use Pdftotext (part of Xpdf, found here). If you pass a non-PDF to pdftotext, it will certainly bark at you, and you can use commands.getstatusoutput to get the output and parse it for these warnings.

If you’re looking for a platform-independent solution, you might be able to make use of pyPdf.

Edit: It’s not elegant, but it looks like pyPdf’s PdfFileReader will throw an IOError(22) if you attempt to load a non-PDF.

In a project if mine I need to check for the mime type of some uploaded file. I simply use the file command like this:

from subprocess import Popen, PIPE
filetype = Popen("/usr/bin/file -b --mime -", shell=True, stdout=PIPE, stdin=PIPE).communicate(file.read(1024))[0].strip()

You of course might want to move the actual command into some configuration file as also command line options vary among operating systems (e.g. mac).

If you just need to know whether it’s a PDF or not and do not need to process it anyway I think the file command is a faster solution than a lib. Doing it by hand is of course also possible but the file command gives you maybe more flexibility if you want to check for different types.

By valid do you mean that it can be displayed by a PDF viewer, or that the text can be extracted? They are two very different things.

If you just want to check that it really is a PDF file that has been uploaded then the pyPDF solution, or something similar, will work.

If, however, you want to check that the text can be extracted then you have found a whole world of pain! Using pdftotext would be a simple solution that would work in a majority of cases but it is by no means 100% successful. We have found many examples of PDFs that pdftotext cannot extract from but Java libraries such as iText and PDFBox can.

The current solution (as of 2023) is to use pypdf and catch exceptions (and possibly analyze reader.metadata)

from pypdf import PdfReader
from pypdf.errors import PdfReadError

with open("testfile.txt", "w") as f:
    f.write("hello world!")

try:
    PdfReader("testfile.txt")
except PdfReadError:
    print("invalid PDF file")
else:
    pass

I run into the same problem but was not forced to use a programming language to manage this task. I used pyPDF but was not efficient for me as it hangs infinitely on some corrupted files.

However, I found this software useful till now.

Good luck with it.

https://sourceforge.net/projects/corruptedpdfinder/

Here is a solution using pdfminersix, which can be installed with pip install pdfminer.six:

from pdfminer.high_level import extract_text

def is_pdf(path_to_file):
    try:
        extract_text(path_to_file)
        return True
    except:
        return False

You can also use filetype (pip install filetype):

import filetype

def is_pdf(path_to_file):
    return filetype.guess(path_to_file).mime == 'application/pdf'

Neither of these solutions is ideal.

1. The problem with the filetype solution is that it doesn’t tell you if the PDF itself is readable or not. It will tell you if the file is a PDF, but it could be a corrupt PDF.
2. The pdfminer solution should only return True if the PDF is actually readable. But it is a big library and seems like overkill for such a simple function.

I’ve started another thread here asking how to check if a file is a valid PDF without using a library (or using a smaller one).