I've never looked into the PDF format, but, does it not allow for annotations that say, "the glyphs in the rectangle ((x0, y0), (x1, y1)) represent the text 'fo

I've never looked into the PDF format, but, does it not allow for annotations that say, "the glyphs in the rectangle ((x0, y0), (x1, y1)) represent the text 'foobar'")? That's been my mental model for how they are text-searchable.