I’d imagine by checking that text is in the drawable area of the PDF, above some font size, at the maximum z height, colour different from the background, etc etc etc.

Though I think this sort of prompt injection is actually very difficult to parse for solely because you could also just put it into a body of text.

Your recruiter is only skimming your resume, a quick parenthetical in the middle of a paragraph won’t be noticed.

Will get a chuckle at the interview though, but now you have a foot in the door!

Convert to bitmap, then OCR again.