Making an anonymous PDF file using PDFLaTeX

Question

When writing a referee report for a journal, it would be preferrable to have the resulting PDF file generated by pdflatex be completely anonymous.

Does one need to take special actions to ensure this? For example, if any references to file names with their paths are included anywhere in the resulting file, that will result in information (my home directory is /home/mariano/... for example)

Answer 1

I guess the path you see is not really written in your PDF, but it is the relative path where the PDF is currently located. Apart from general information of the PDF producer ("LaTeX with hyperref package", etc.) I see no private information when examining the file with Adobe Acrobat Pro. (In this sense, PDFs produced with PDFLaTeX and XeLaTeX are more anonymous than those produced by, say, MS Word.)

However, if you wish to erase even that, you can try

\usepackage{hyperref}
\hypersetup{
  pdfinfo={
  pdfproducer={},
  Title={},
  Subject={},
  Author={},
  }
}

(for all keys described in § 3.9 of the hyperref package documentation).

---

Using Werner's suggestion---of which I was completely unaware---you can accomplish the same directly with the PDFTeX engine, thus:

\pdfinfo{
  /Title ()
  /Creator ()
  /Producer ()
  /Author ()
  /Subject ()
  /Keywords ()
}

Yet I'm a bit puzzled with this slashed syntax (instead of the TeX backslash).

Answer 2

pdfTeX and luaTeX write additional information into the resulting PDF as documented in pdftex-pdfkeys.pdf:

1. The Document Catalog contains an additional key PTEX.Fullbanner which contains the full version of pdftex/luatex, i.e. "This is pdfTeX, Version 3.1415926-2.4-1.40.13 (TeX Live 2012) kpathsea version 6.1.0)". This key can be seen in some version of Adobe Reader and Adobe Acrobat (Document Properties -> Advanced).

For every included image theses keys are added to the XObject containing the image:

1. PTEX.FileName is the filename as seen by pdfTeX, e.g. "./sample2e.pdf"
2. PTEX.PageNumber is the page number of an included PDF
3. PTEX.InfoDict is a copy of the Info Dictionary (e.g. Title, Author, etc.) of an included PDF.

There is currently no way to disable the writing of these keys.

If you want to remove these keys from a PDF, the easiest way is probably a conversion to PostScript followed by a conversion to PDF.

Answer 3

First of all, PDF is not like DOC or XLS – I have never encountered an path names or other "hidden" information in it that reveals details about my computer or environment. Apparently I was wrong, pdftex und luatex do write extra information into the PDF's object catalog! See answer of Martin for details.

Nevertheless, at times we all face a bit of paranoia. A simple, albeit brute-force approach in this case is to just rasterize the complete PDF (here using ImageMagick):

convert -density 300 report.pdf report-anonymized.pdf

The disadvantage is, of course, that the resulting PDF can become fairly big and that it is no longer possible to select text in it.

A bit less drastic is the conversion PS and back to PDF, as suggested by Mariano (here using Ghostscript):

pdf2ps report.pdf - | ps2pdf - report-anonymized.pdf

This also leads to a complete recoding of the PDF. (I use this approach frequently to "sanitze" PDF with transparencies generated by OpenOffice, on which pdflatex often chokes).

Answer 4

I can think of two possibilities, none unfortunately pdfLaTeX-based. First, I can add to the reply by @daniel by mentioning PStill with its PDF to raster plugin PDF2R. This converts the pdf to a raster pdf similarly to what was mentioned for ImageMagick. A second option would be to generate a PS-file and then use ps2pdf to generate the PDF.