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Comment by jwrallie | Hacker News Reader

I learned that a long time ago when I was a student and wanted to submit a pdf generated by a trial version of some software as an assignment and was trying to be clever and cover the watermark that said unregistered with a white box.

When opening the file in my slow computer, I could see all the rendering of the watermark happening in slow motion until the white box would pop up on top of the text.

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When I was a student, and using a shareware or trial version of some software and wanted some printed output from it without a watermark, I printed to postscript (chose a printer that supported postscript and the driver used it instead of rasterized images), but using a file instead of a printer.

I could then open up the postscript, delete the commands that rendered the watermark, save it, then I converted it to PDF so it would be easy to print.

You don't need PostScript for that. The PDF text commands are Tj and TJ, and rarely ' and ". They are easy to delete without going through PostScript. Tj means showing a simple text string. TJ means showing an array of strings possibly with space adjustments. ' means moving to the next line and showing a simple string. " means doing that and setting character spacing.

Perhaps, but it's easier to open up and edit a .ps file in a text editor than a PDF. PDF is a binary format with compressed streams, while postscript is just a stack-oriented programming language.

Tools like qpdf makes it easy to edit a .pdf file in a text editor too. I’d argue using such tools is easier than and simpler than printing to postscript.

Sure. I've not tried it. Was it around in 2002? Because that's when my story occured.

It's actually quite easy to open the pdf and see that there are several different elements per page to the document, eg the main text, an image, the footer, the title.

Randomly removing these by trial and error will usually quite easily allow you to find the watermark and nix it, with the advantage that even a sophisticated recipient will not be able to find out from the pdf file what the watermark was.

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