Hide information in a PDF file in Python

Question

In Python, I have files generated by ReportLab. Now, i need to extract some pages from that PDF and hide confidential information.

I can create a PDF file with blacked-out spots and use pyPdf to mergePage, but people can still select and copy-paste the information under the blacked-out spots.

Is there a way to make those spots completely confidential?

Per example, I need to hide addresses on the pages, how would i do it?

Thanks,

smilingthax · Accepted Answer · 2010-11-02 22:52:16Z

1

Basically you'll have to remove the corresponding text drawing commands in the PDF's page content stream. It's much easier to generate the pages twice, once with the confidential information, once without them.

It might be possible (I don't know ReportLab enough) to specially craft the PDF in a way that the confidential information is easier accessible (e.g. as separate XObjects) for deletion. Still you'd have to do pretty low-level operations on the PDF -- which I would advise against.

answered Nov 2, 2010 at 22:52

smilingthax

5,8741 gold badge26 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Danosaure · Accepted Answer · 2010-11-02 23:30:20Z

0

(Sorry, I was not able to log on when I posted the question...)

Unfortunately, the document cannot be regenerated at will (context sensitive), and those PDF files (about 35) are 3000+ pages.

I was thinking about using pdf2ps and pdf2ps back, but there is a lot of quality.

pdf2ps -dLanguageLevel=3 input.pdf - | ps2pdf14 - output.pdf

And if i use "pdftops" instead, the text is still selectable. If there is a way to make it non-selectable like with "pdf2ps" but with better quality, it will do too.

answered Nov 2, 2010 at 23:30

Danosaure

3,6654 gold badges30 silver badges43 bronze badges

4 Comments

smilingthax Over a year ago

Non-selectable might not be consistent across different pdf viewers, e.g. pdftotext extracts it, but Adobe Reader doesn't, etc. If this is sensitive information, you'll have to remove it completely. Everything else can be circumvented, more or less easily. You might be able to write a regular expression to remove the critical lines from the .ps representation, though (and keep quality by using the right options [try pdf2ps and pdftops, etc.]).

Danosaure Over a year ago

I have never worked with PS files before (beside converting them)... I guess I can always give it a try. I'll get back with my findings.

smilingthax Over a year ago

I think what happens with pdf2ps is that the fonts are either converted to Bitmap-fonts, or converted to paths (in which case the font would print fine, it only looks bad on screen). Because of reencoding, and if a inverse table is not included, it's pretty hard to find the glyphid to character correspondence automatically. As soon as the text looks fine (e.g. pdftops), Type1 or TrueType fonts are used, and the glyph-to-char correspondence is essentially known, which also means that extracting the text is "easy". If the font is reencoded, obfuscation by stripping some tables could be possible.

Danosaure Over a year ago

Thanks, I ended up converting "pdftops -level3 file.pdf file.ps", open('file.ps', 'rb'), process the file into StringIO, dump the StringIO back to 'file.ps', and reconverting "ps2pdf file.ps file.pdf" and the output is what I want. Thanks for the help.

Collectives™ on Stack Overflow

Hide information in a PDF file in Python

2 Answers 2

Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related