PSA: PDFs leak data

Lucy just noticed that a PDF she was viewing in her browser revealed something about its history when she hovered over the browser tab. In her case, harmless enough: the shameful fact that she created one of her lovely Excel summary sheets in PowerPoint. (Not even Keynote!)

Screenshot of a Firefox tab which has a PDF open. The tab reveals the inner 'title' of the PDF, which in turn reveals Lucy's shame: that she created it in PowerPoint.

PDFs are full of invisible data

Chock-full of it. Here's how this can trip you up. Let's say Jim is leaving so the team writes him a lovely message. Nobody really likes Jim, so you save the file on your Desktop with a snarky title.

Screenshot of a Word doc. The text wishes Jim well, but the document's title on disk is 'We all hate Jim really because he's a piece of work'.

Then you Print > Save as PDF…, and of course you save the file as Good luck Jim!.pdf.

Screenshot of us saving as PDF. We've renamed the PDF as it will be saved on disk, but forgotten about its 'title'.

Oooh but you didn't notice the Title field there, and now that's embedded in the PDF. Jim can just inspect the file or, if you're unlucky, he'll open it in Firefox on the farewell Zoom call and it'll be visible to everyone. Em-barrassing!

Screenshot of the macOS file info pane clearly showing the original file title.

You think this will never happen to you? Oh sweet child, it happens all the time. And there's not really much you can do about it other than be aware of it, and remember not to do it.

PDFs contain a lot more information than you can see. Be careful.