pdf-redactor

A general-purpose PDF text-layer redaction tool, in pure Python, by Joshua Tauberer and Antoine McGrath.

pdf-redactor uses pdfrw under the hood to parse and write out the PDF.

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This Python module is a general tool to help you automatically redact text from PDFs. The tool operates on:

• the text layer of the document's pages (content stream text)
• the Document Information Dictionary, a.k.a. the PDF metadata like Title and Author
• embedded XMP metadata, if present

Graphical elements, images, and other embedded resources are not touched.

You can:

• Use regular expressions to perform text substitution on the text layer (e.g. replace social security numbers with "XXX-XX-XXXX").
• Rewrite, remove, or add new metadata fields on a field-by-field basis (e.g. wipe out all metadata except for certain fields).
• Rewrite, remove, or add XML metadata using functions that operate on the parsed XMP DOM (e.g. wipe out XMP metadata).

How to use pdf-redactor

Get this module and then install its dependencies with:

pip3 install -r requirements.txt

pdf_redactor.py processes a PDF given on standard input and writes a new, redacted PDF to standard output:

python3 pdf_redactor.py < document.pdf > document-redacted.pdf

However, you should use the pdf_redactor module as a library and pass in text filtering functions written in Python, since the command-line version of the tool does not yet actually do anything to the PDF. The example.py script shows how to redact Social Security Numbers:

python3 example.py < tests/test-ssns.pdf > document-redacted.pdf

Limitations

Content Stream Compression

Because pdfrw doesn't support all content stream compression methods, you should use a tool like qpdf to decompress the PDF prior to using this tool, and then to re-compress and web-optimize (linearize) the PDF after. The full command would be something like:

qpdf --stream-data=uncompress document.pdf - \
 | python3 pdf_redactor.py > /tmp/temp.pdf
 && qpdf --linearize /tmp/temp.pdf document-redacted.pdf

(qpdf's first argument can't be standard input, unfortunately, so a one-liner isn't possible.)

Other limitations

This tool has a limited understanding of glyph-to-Unicode codepoint mappings.

pdfrw is also kind of broken in Python 3 because it improperly round-trips the entire PDF through Latin-1 encoding. I've monkey-patched it here and done some tricks to get around it. While I recommend sticking with Python 3, this module should also work with Python 2.

Testing that it worked

If you're redacting metadata, you should check the output using pdfinfo from the poppler-utils package:

# check that the metadata is fully redacted
pdfinfo -meta document-redacted.pdf