You redacted the body of the document perfectly. The visible text is clean. But the file's metadata still says 'Author: John Smith, Path: /Users/jsmith/Drafts/SettlementProposal_v3.pdf'. The settlement amount might be redacted; the fact that there were three drafts isn't.
What metadata a PDF carries
A typical PDF includes:
- Document properties: title, author, subject, keywords. - Application info: producer (software that made the PDF), creator (originating application). - Timestamps: creation date, modification date. - File path: sometimes stored in producer/creator strings. - XMP packet: extended metadata in XML, can include comments, version history, edit history. - Annotations and comments: even removed annotations sometimes leave traces. - Embedded files: fonts, images, attached files.
How metadata leaks
Released government documents have revealed: the laptop username of the drafter, the file's original location on a network drive, the version number (showing a v3 implies v1 and v2 exist), comments from earlier drafts marked privileged.
For public releases and FOIA responses, metadata is the second redaction pass. Skip it and the body redactions are undermined.
How to strip metadata
Most tools have a 'remove personal information' or 'sanitise document' option. Acrobat: Tools → Redact → Remove Hidden Information. Flint's edit tool supports metadata removal as part of cleaning a document.
For batch processing, command-line tools (exiftool, qpdf) can strip metadata across many files. Always verify by opening document properties after stripping.
Render-and-re-OCR for ultra-clean output
For very sensitive releases, render the PDF to images and re-OCR to produce a new text layer with no historical metadata. This is destructive of structure (links and bookmarks are lost) but produces the cleanest possible output.
Reserve this for high-stakes releases. For routine documents, metadata stripping via a sanitise option is usually enough.
FAQ
Does Print to PDF strip metadata?
Mostly — print-to-PDF usually produces a fresh PDF with minimal carry-over metadata. Some printers preserve title/author from the source. Verify.
Will saving in Acrobat preserve metadata?
Yes by default. Use 'Save As' with the sanitise option to strip. Plain Save preserves.
Can metadata be cryptographically signed?
Yes — signed PDFs include metadata in the signed region. Tampering with metadata can invalidate the signature, which is sometimes a feature.
Does Flint's redaction tool strip metadata?
The redaction tool focuses on content. Use Flint's edit tool for metadata cleaning as a separate step.
Metadata is the second pass. Strip it whenever you redact. Clean your PDFs in Flint before release.