LibreOffice PII Anonymization Extension

LibreOffice PII Anonymization Extension

LibreOffice has an estimated 200 million users worldwide. Governments, schools, and businesses all rely on it. Many use it to avoid costly software licenses. But until now, users had no built-in tool to find and remove personal data from their files.

The old fix was painful. Copy text into a web app. Anonymize it. Paste it back. This kills formatting. It breaks tables, styles, and layout. For complex Writer documents, this does not work.

The anonym.legal extension solves this. It works inside the app. It detects 267+ entity types in Writer, Calc, and Impress.

Install in Under Two Minutes

The extension ships as an .oxt file. This is the standard format for all extensions.

Quick Install:

1. Download the .oxt from anonym.legal/api/download/libreoffice
2. Double-click the file
3. Confirm the prompt
4. Restart

Manual Install:

1. Open the application
2. Go to Tools, then Extension Manager
3. Click Add, then pick the .oxt file
4. Restart

After restart, the anonym.legal sidebar shows under View, then Sidebar. Sign in to begin.

How Detection Works

Two engines run together to find PII.

Detection runs on the anonym.legal API. Text goes to certified servers in Germany. The servers hold ISO 27001 status. Results return to the extension. No document files are sent. Only text is transmitted.

What each app does:

• Writer: Extracts full text or selection only
• Calc: Reads cells as tab-separated values across all sheets
• Impress: Reads text objects from all slides

Five Anonymization Methods

You can mix methods in one pass. Replace names, but encrypt emails. Each entity type gets its own rule.

Format Stays Intact in Writer

This is the key win over copy-paste. The extension keeps all formatting when it replaces text.

Seven font properties preserved:

• Family, size, bold, italic, color, underline, strikethrough

Four paragraph properties preserved:

• Alignment, first-line indent, left margin, right margin

"John Smith" in bold 14pt Times New Roman becomes "PERSON" in the same style. Tables, headers, and footers all stay intact. The extension works inside the document model. It does not export and reimport text.

Note: Format tracking only applies to Writer. Calc and Impress do text-level replacement only.

Review Before You Apply

The preview shows up to 50 found entities. Each row shows:

• Entity type (PERSON, EMAIL_ADDRESS, PHONE_NUMBER, etc.)
• Original text
• Proposed replacement
• Confidence score

Accept or reject each entity one by one. Select all or clear all with one click. Nothing changes until you click Apply. In Writer, Ctrl+Z undoes the last operation.

Presets Sync Across Devices

Save your settings as a preset. Pick entity types, methods, and thresholds. Reuse it across all your documents. It saves time.

On paid plans, presets sync across all anonym.legal products. Set one up in the web app. It appears in the desktop app and the Office Add-in within five minutes. Encryption keys use zero-knowledge wrapping. Only your password can decrypt them.

For more on how the Office Add-in handles the same workflow in Word, see Word Add-in Redaction for Law Firms.

LibreOffice vs. Microsoft Office

Both extensions share the same backend. The same text gives the same results in Writer and in Word. The engine is one and the same.

For a broader look at PII compliance across operating systems, see Cross-Platform PII Compliance: Mac, Linux, Windows.

System Requirements

• LibreOffice 3.0 or later
• Python 3 (bundled with most installs)
• Internet access (for the PII detection API)
• anonym.legal account (free tier: 200 tokens/month)

Get Started

1. Download the extension
2. Double-click to install, then restart
3. Open View → Sidebar → anonym.legal panel
4. Sign in
5. Open a document, click Analyze, review, click Apply

Full docs: LibreOffice Extension Docs

When This Approach Has Limits

Working inside the document model to preserve formatting is what makes this extension better than copy-paste, and that design is sound, but limits remain worth stating plainly.

Detection accuracy bounds the result. The two engines find what they are trained to find. Regex catches structured patterns like emails and IBANs with high confidence, but spaCy NLP scores names, organizations, and locations at 0.85 and above, which means borderline cases fall below threshold and slip through. A name written in an unusual form, a misspelled location, or a free-text note can be missed entirely. The preview shows up to 50 entities, so longer documents with more matches still require you to verify that nothing was overlooked before you apply changes.

Format preservation is Writer-only. The seven font and four paragraph properties are tracked in Writer through the UNO model, but Calc and Impress do plain text-level replacement. A spreadsheet anonymized through this extension keeps no record of cell styling decisions, and quasi-identifiers spread across columns, such as postcode plus birthdate plus role, can re-identify a person even after direct identifiers are gone. The output may be pseudonymized rather than truly anonymized, which carries legal consequences worth understanding before sharing.

Encrypt mode keeps data in legal scope. The Hash and Encrypt methods are pseudonymization under GDPR Article 4(5), not anonymization. Encrypted values remain reversible with your key, so the data stays inside GDPR scope and the burden simply shifts to protecting that key custody. The extension supports your compliance workflow but does not constitute compliance on its own. A human still has to choose the right method per entity type, confirm the preview, and judge whether the shared copy meets the legal standard the situation demands.

Sources

• The Document Foundation — estimated 200M+ LibreOffice users worldwide
• anonym.legal PII Detection Testing — 95.5% accuracy, 42/44 independent tests
• GDPR Recital 26 — anonymization removes data from GDPR scope; Article 4(5) — pseudonymization definition