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Short, practical explainers on redaction, hidden file data, signatures, and checking what a tool does with your files. Each one starts with the answer, then shows how to check it yourself.

• We tested 6 free PDF redaction tools. 4 left the SSN in the file.

  A reproducible test of six free redaction tools: what each one actually removed, and what it left in the file.

• Is covering text with a black box real redaction?

  Why a black rectangle over PDF text usually hides nothing, and what real redaction removes.

• How to check that a PDF is properly redacted

  A step-by-step checklist for confirming that redacted content can’t be recovered.

• Does removing EXIF data remove GPS location from a photo?

  Where a photo’s location lives, what stripping removes, and how to check the result.

• What hidden data is in a PDF?

  Metadata, comments, attachments, scripts, and old revisions a PDF can carry beyond its pages.

• Redacting PHI for HIPAA: the 18 Safe Harbor identifiers

  The 18 Safe Harbor identifiers, de-identification versus redaction, and a document checklist.

• How to redact audio and video: spoken details, faces, and on-screen text

  Muting spoken details, covering faces and on-screen text, and stripping media metadata.

• What is a PAdES signature, and what does a document seal prove?

  How PDF digital signatures and timestamps work, and the limits of what they prove.

• How to verify a signed PDF

  What a signature validator checks, and how to read the result.

• Are online PDF tools safe? How to tell if a tool uploads your file

  Checking with DevTools whether a web tool sends your file to a server.

• What is a SHA-256 checksum, and what does it prove?

  What a file’s SHA-256 fingerprint proves, and how to compute and compare one.