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ntg-pdftex@ntg.nl

June 2015

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Deterministic PDFs (switch to disable addition of timestamps and random ID nonces)
by Markus Kuhn 26 Jun '15

26 Jun '15

For some applications, especially where the output of pdftex lives in any kind of version-control system, it would be extremely helpful to have a switch that causes pdftex to output deterministic PDF files. At present, there are three fields in each PDF generated by pdfTeX that change at each run on identical source files: $ pdftex '\hbox{}\vfill\eject\end' Output written on texput.pdf (1 page, 8182 bytes). $ mv texput.pdf texput2.pdf $ pdftex '\hbox{}\vfill\eject\end' Output written on texput.pdf (1 page, 8182 bytes). $ diff -a texput.pdf texput2.pdf 51,52c51,52 < /CreationDate (D:20150619105331+01'00') < /ModDate (D:20150619105331+01'00') --- > /CreationDate (D:20150619105323+01'00') > /ModDate (D:20150619105323+01'00') 76c76 < /ID [<BA26D54E6C14BF8195356C4A7162A40A> <BA26D54E6C14BF8195356C4A7162A40A>] --- > /ID [<D5B098C606C27E75987095F36CDCFED7> <D5B098C606C27E75987095F36CDCFED7>] Looking at the PDF 1.7 specification in ISO 32000 at http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_20… I believe that all these non-deterministic elements are optional, and could be suppressed without violating the PDF specification: Table 317 on page 550 says that the CreatingDate entry of the document information directory is optional, and the ModDate entry is optional unless PieceInfo is present. Pdftex does not output PieceInfo, right? So ModDate is also optional here. Likewise, the ID element appears to be optional as long as the PDF document is not encrypted. For DVI mode, we have already "-output-comment ''" to suppress the addition of a timestamp. Feature request: Would it be possible to add a switch, for example a command-line option like "-deterministic-output" that suppresses the automatic addition of timestamps and random ID byte strings to the generated PDF, such that repeated runs of pdftex produce identical output? Thanks, Markus -- Markus Kuhn, Computer Laboratory, University of Cambridge http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain

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