For months the OCR on this site returned a file. It took a believable four or five seconds, reported no error, and handed back a PDF of the right page count. The text layer inside it was empty. Nobody complained, because there was nothing to complain about. A searchable PDF with no searchable text looks exactly like a searchable PDF until you press Ctrl+F. It took a benchmark harness with a ground-truth word list to notice, and what it found was one number that explained everything: ...