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PNG would be more fitting for content like this.

(In case folks don't know, PNG better for text because JPG's compression introduces "ringing" artifacts around sharp edges, such as the black/white transition of text.) https://en.wikipedia.org/wiki/Ringing_artifacts

JPGs are also a lot safer as PDFs can ping remote resources using carefully hidden beacon images.

Although that said, I sometimes use this to see who opened my files. I once left hundreds of these on a very popular cloud hosting provider (not naming names), and somebody working there was stupid to open the PDF on a machine connected to the internet, thereby proving abuse by employees and proving any random stranger can access 'your' files in the so called 'cloud'.

Look up 'honeydocs'. Some interesting articles about this technique

Is that effective for non-adobe pdf viewers? What about the ones that disable javascript?

Look into canarytokens. Plenty of file types that do not rely on JavaScript nor macros etc

Maybe it was an indexer that for whatever reason runs the full PDF handling code?

Are the contents of the link so very pixelated that you are unable to follow along without PNG conversion? If yes, may I recommend a quick trip to your local optometrist?

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