Most PDF editors can only change text that still has a live text layer, and the new words rarely match. PDFKiller also works on scans. It measures the font, spacing, ink, blur and paper grain from the page and rebuilds just the edited words, keeping the original JPEG compression. Every edit is re-read with OCR and scored, and you check it at 800% before exporting. Try the samples free without an account; your first 5 PDFs are free too.