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Every legacy .xls/.doc is a CFB/OLE2 file, so the signature alone isn't encryption. Walk the compound file's directory (bounds-checked, bounded loops; raw UTF-16 scan when the structure is unreadable) and report Encrypted only for an EncryptedPackage/EncryptionInfo stream; other compound files are LegacyBinary with a "save as .xlsx" message. Tests build CFB bytes in code. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>