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Image poisoning’s general principle is to change pixels in a way were our eye can’t notice, but that screw up the labeling by LLMs.
You can probably try to apply the same principle, poison the PDF in a way that only humans can read it.
Thing is, I assume you distribute your content on PDFs to make the content accessible to humans. That usually means having the text embedded for easy copy-paste and similar methods. Poisoning these might end up being counterproductive for your objective.
All this to say that No, I have no idea of a poisoning algorithm for PDFs
No idea with Japanese, but in Spain, most audiovisual media is dubbed.
Comedy is adapted according to context, both the plot’s context and the current cultural context. Jokes are changed to fit the scene AND the translation.
When you start watching them in their original language, usually English, you find that the OG is usually better. And I say usually because in rare occasions, the joke in Spanish ends up being better, at least IMO.