Free redaction tools remove a value permanently from the copy they produce, and several run on your device. That destruction is the point of the category. Masking covers a value while keeping a way back to it. Choose by whether you will need the original again, not by which word the tool uses.
What a redactor actually does to the file
The good ones remove the underlying content rather than paint over it, and their own documentation is unusually clear about the difference. Adobe's guidance frames the job as permanently removing sensitive content and hidden data so it is not passed along when the PDF is published. PDF24 states that redactions made with its tool are permanent and cannot be undone, and that affected pages are converted to images so the original page content is replaced outright.
The failure this category exists to prevent is the drawn rectangle. A shape placed over text is an annotation sitting above content that is still in the file, recoverable by anyone who selects and copies it. That is why Stirling PDF distinguishes automatic redaction, which deletes the matching text from the file, from a manually drawn box, and recommends keeping its convert-to-image option enabled so no recoverable text remains underneath.
Which tool does what
Each row below states only what that product's own current documentation says. Where a vendor is silent, the cell says so rather than guessing, because silence is not evidence either way.
| Tool | Removes content | Where it runs | What finds the values | Cost and account |
|---|---|---|---|---|
| Adobe Acrobat | Yes, and its docs separate applying redactions from marking content | Not stated on the page reviewed | You select content, or supply a word or pattern to search for | Paid tiers only |
| Apple Preview | Yes; the redaction becomes permanent once the document is closed | Not stated on the page reviewed | You select the text yourself | Included with the operating system |
| PDF24 Creator | Yes, and pages are rasterized so content is replaced | Desktop app that works offline, files stay on your PC | You blacken each area with a pen or a shape | Free, no registration |
| PDF24 online tool | Yes, same mechanism | Runs on the vendor's servers in the cloud | You blacken each area with a pen or a shape | Free, no registration |
| Stirling PDF | Yes for automatic redaction; manual boxes need the image conversion | Self-hosted, on infrastructure you run | You type each word or pattern, or draw the boxes | Free and open source |
| LibreOffice Draw | Yes in the exported copy; the source document is left unchanged | Not stated on the page reviewed | You draw rectangles or freeform shapes over the content | Free and open source |
One absence is worth naming because people look for it: Microsoft Word has no redaction feature. What it documents is Document Inspector, which strips comments, hidden text, tracked changes, and metadata. That is a different job from blacking out visible body text, and treating it as redaction is a way to ship a document you believed was covered.
Every one of them makes you find the values yourself
Look down the fourth column and the pattern is the same everywhere. Apple documents a tool where you select the text to remove it from view. LibreOffice asks you to mark content by drawing rectangles or freeform shapes over it. Adobe lets you select content or search for a word, a phrase, or a pattern that you supply. Even the option Stirling PDF calls automatic searches for the text you specify, one word or pattern at a time.
None of them reads a document and tells you what is sensitive in it. That is the real cost of a free redactor, and it is not the licence fee. On a referral letter or a discharge summary the names, dates of birth, chart numbers, phone numbers, and addresses are scattered through running prose, repeated in headers, and split across table columns. Marking them by hand is slow, and the ones you miss are the ones that ship.
Two traps worth knowing
The first is the word "online". PDF24 is a useful example precisely because it is honest about it: the desktop Creator works offline and keeps files on your PC, while the browser tool at the same brand runs on the vendor's servers. Same vendor, same feature, entirely different answer to "did the document leave my machine".
The second is LibreOffice's design: redaction produces a separate exported copy and the source document is not affected. That is reasonable behaviour and it means the file sitting in your folder with the familiar name is still the unredacted one.
When a free redactor is the better choice
Destructive redaction is the right tool, not a fallback, in several concrete situations:
- the recipient must never be able to recover the covered value, as in a public records release or a document produced to an opposing party;
- a retention or court rule requires the identifier to be gone from that specific file;
- you have no further use for the original in that document, so a way back adds a step with no benefit.
In each of those a reversible copy is the wrong tool, because it leaves open exactly the recoverability the situation is designed to prevent.
Where PHI Mask fits
PHI Mask does the finding. Open a document and it marks the names, dates, chart and account numbers, phone numbers, addresses, and other identifiers it detects, ready for you to accept or change. There is no list to type and no rectangle to drag for the fortieth identifier on page three. Detection results are published per document type on the benchmark, scored against a public corpus of authored documents rather than asserted in a sentence.
It reads the awkward formats too. Screenshots and scanned PDFs are where hand-marking gets slowest and where text-only tools have nothing to work with, so PHI Mask reads the page itself and follows multi-column layouts, tables, and interface chrome. Pasted text, a screenshot, and a PDF all go through the same pass, in the same browser tab, instead of three products with three habits.
And it does the thing destructive redaction cannot. The map between real values and their stand-ins stays in that tab, so a covered copy can go out for review or into an assistant and the reply comes back restorable in one step. When a value should never return, PHI Mask redacts without stand-ins too. Both jobs, one tool, no install.
Review before sharing.
Start with text, a PDF, or a screenshot.
Sources and review notes
Each product statement above comes from that vendor's own current documentation, reviewed on the date shown at the top of this page: Adobe, Apple, PDF24, Stirling PDF, LibreOffice, and Microsoft. Products change; this comparison carries a recheck date for that reason.
Common questions
- Is drawing a black box the same as redacting?
- No. A drawn shape is an annotation sitting above content that is still in the file and can be selected and copied. Tools that redact properly remove the content or replace the page with an image.
- Does Microsoft Word redact documents?
- Its documentation describes Document Inspector, which removes comments, hidden text, tracked changes, and metadata. That is a different job from removing visible body text.
- Does an online redaction tool keep my file on my machine?
- Not necessarily, and the same brand can answer differently for two of its own products. One vendor documents a desktop app that works offline alongside a browser tool that runs on its servers. Check which one you opened.
- Do free redaction tools find the sensitive information for me?
- No. Every tool compared here has you select the content, type the words to search for, or draw over each item. PHI Mask detects names, dates, and identifiers across text, screenshots, and PDFs and presents them for review, which is where the time goes on a long document.
- Can I use a free redactor and PHI Mask on the same document?
- Yes, and in sequence they solve different problems. Cover a working copy for review or reuse, then apply destructive redaction to whichever copy is the final one that must never be reversed.
- If I mask a document and never restore it, is that redaction?
- Not quite. The value is absent from the copy you share either way, but with masking a map still exists in the tab that created it. A destructive redaction leaves no map anywhere.