It reads the file, not just the filename
Most renaming tools shuffle the characters you already have. Magic Rename opens the document and reads it: the text of a PDF, the cells of a spreadsheet, the slides of a deck, the words inside a photo of a receipt. The new name comes from the content, which is why it can tell an invoice from a statement from a contract when all three arrived as Scan_0043.pdf. Scanned pages and photos are read with on-device OCR, so a picture of a receipt is renamed as accurately as a text PDF.
