Good catch on the average-word-length heuristic, though it can still pass while being wrong: two-column academic PDFs run through the same kind of converters sometimes come out with correct spacing but scrambled reading order, column A then column B interleaved wrong, and the average stays around 5.5 chars because the words themselves are intact, it's just the sequence that's broken. Worth pairing the length check with something order-sensitive rather than relying on it alone. Also curious about pymupdf4llm's page markers on rotated or scanned pages, have you checked those against the real page breaks, or just on clean digital PDFs like the arXiv one here?