That's not an unsolvable problem. Checking visibility is easy, computer graphics have been doing this since forever. Fonts that are too small, ditto. Contrast is well understood.
replyIf you do want to render, you don't have to do the convoluted PDF route. That's what the user would do, the software would just use its normal drawing code. OCR is neither needed nor desirable. OCR errors would erroneously flag perfectly normal text, and it can be fooled just like a human can. You can detect whether or not there's any rendering with the bounding box of whatever text section you are looking for (something Word already has to calculate if it wants to render correctly on screen).
I'm only talking about checking for visible text. This will not solve the larger problem of malicious AI instructions.
Embed text in an image, a human will read it just fine. Perfectly visible but opaque to AI. It'd be obnoxious to turn it into an attack, but you can replace letters with images in phrases so that humans read "she believed" while AI reads "he lied."
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