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Asked: 2026-05-11T07:03:37+00:00

I get a file via a HTTP upload and need to make sure its

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I get a file via a HTTP upload and need to make sure its a PDF file. The programing language is Python, but this should not matter.

I thought of the following solutions:

  1. Check if the first bytes of the string are %PDF. This is not a good check but prevents the user from uploading other files accidentally.

  2. Use libmagic (the file command in bash uses it). This does exactly the same check as in (1)

  3. Use a library to try to read the page count out of the file. If the lib is able to read a page count it should be a valid PDF file. Problem: I don’t know a Python library that can do this

Are there solutions using a library or another trick?

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1 Answer

  1. The two most commonly used PDF libraries for Python are:

    Both are pure python so should be easy to install as well be cross-platform.

    With pypdf it would probably be as simple as doing:

    from pypdf import PdfReader reader = PdfReader("upload.pdf")

    This should be enough, but reader will now have the metadata and pages attributes if you want to do further checking.

    As Carl answered, pdftotext is also a good solution, and would probably be faster on very large documents (especially ones with many cross-references). However it might be a little slower on small PDF’s due to system overhead of forking a new process, etc.

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