The most common way to redact a PDF does not redact anything. It draws an opaque shape over text that remains in the file underneath.
What a white box actually does
PDF content is layered. Drawing a filled rectangle adds a graphic that paints over what was drawn before it, in the same way a sticker covers print on paper — except the paper underneath is still readable by anything that does not rely on light.
Select the area and copy it. The hidden text appears in the paste. Search the document for a covered word and it is found. Extract the text and it is all there.
This is not obscure. Government departments, law firms and newspapers have all published documents redacted this way and had the covered content recovered within hours, because recovering it takes a copy and a paste. If the reason for covering something is that it must not be read, a drawn shape is not a mechanism.
Removing content properly
| Method | Removes content? | Cost |
|---|---|---|
| White or black rectangle | No — still fully recoverable | None |
| Redaction tool | Yes — deletes the objects | Needs a proper editor |
| Flatten page to image | Yes — no text remains | Loses all selectable text |
| Edit the source, re-export | Yes | Needs the original file |
| Print and rescan | Yes | Crude, but genuinely effective |
The flatten route is the one available without specialist software, and it is reliable precisely because it is blunt. Rasterise the page, place the covering shape on the image, and the text is gone because the page is now a picture. PDF to JPG converts pages in the browser, and the result can be rebuilt into a PDF afterwards.
What else survives redaction
Removing the visible text is necessary and not always sufficient. Several other places in the file can hold the same information.
A properly redacted document with the sender's name still in the metadata, or an earlier draft retained by incremental saving, has not achieved what was intended.
- Document metadata — author, company, original filename, editing software.
- Earlier versions retained by incremental saves. Use Save As to force a full rewrite.
- Comments and annotations, which carry their own text and author names.
- Attachments and embedded files, which are not visible on any page.
- Bookmarks and the document outline, which often quote headings verbatim.
- The OCR text layer beneath a scan, which is separate from the image.
That last one is the subtle case. Covering part of a scanned image hides the picture of the words; the OCR layer underneath still holds them as text. Redacting a scanned document means dealing with both.
Whiting out for ordinary reasons
Not every white box is a redaction. Covering a stray mark on a scan, blanking an outdated price, or hiding a printer artefact are legitimate and carry no secrecy requirement.
For those, a drawn shape is entirely adequate and much simpler. The distinction is whether it would matter if someone recovered what is underneath — and that question should be asked deliberately rather than assumed.
If the answer is that it would matter, treat it as redaction and use one of the methods above. If not, draw the box.
Drawing and annotating
Annotation is a separate mechanism from page content, and the difference is worth understanding because it determines what is reversible.
Annotations — highlights, freehand drawing, notes, stamps, arrows — are stored as objects alongside the page rather than as part of it. They can be moved, edited and deleted individually without touching the underlying document, and a reader that does not display annotations shows the original page unchanged.
- macOS Preview: full markup toolbar built in — draw, highlight, shapes, text, signature.
- iPad and Apple Pencil: the best freehand experience available; annotations save into the PDF.
- Chrome and Edge: both now include basic drawing and highlighting in their built-in viewers.
- Acrobat Reader: free, includes comment and drawing tools on every platform.
Because annotations are separate objects, they can also be stripped. That is useful when circulating a marked-up draft and then needing a clean copy, and it is a hazard if you assumed a drawn shape was permanent — flattening is what makes an annotation part of the page.
Changing colours
Three different requests hide behind "change the colour of a PDF", and only one of them is straightforward.
Inverting for night reading is a viewer setting, not a change to the file. Acrobat has it under accessibility preferences; macOS offers a system-wide Smart Invert. Nothing is modified.
Converting colour to greyscale for cheaper printing is a print setting in the print dialog, and can also be baked into the file by a converter.
Changing the actual colours of page content means editing every object that specifies a colour, and there is no simple route. If a document needs to exist in different colours, produce it from the source rather than recolouring the PDF — that is one of several places where the fixed-layout design of the format is doing exactly what it was intended to do.
Frequently asked questions
Does a white box over text remove it?
No. It draws a graphic on top. The text underneath stays in the file — selectable, searchable and recoverable by copy and paste. Documents redacted this way have been published and un-redacted within hours, repeatedly.
How do I actually redact a PDF?
Use a redaction tool that deletes the underlying objects, or flatten the page to an image so no text remains, or edit the source and re-export. Flattening is the route available without specialist software and is reliable because the page becomes a picture.
What else needs checking after redacting?
Metadata, earlier versions kept by incremental saves, comments and their author names, embedded attachments, the document outline, and the OCR text layer beneath a scan. Covering part of a scanned image hides the picture of the words while the text layer still holds them.
Is a black bar safer than a white box?
No — it is the same mechanism and the same failure. The colour of the covering shape has no bearing on whether the text beneath it remains in the file.
How do I draw on a PDF for free?
macOS Preview has a full markup toolbar, Chrome and Edge both include drawing and highlighting in their built-in viewers, and Acrobat Reader is free on every platform. On an iPad with a Pencil the freehand experience is the best of the lot.
Can annotations be removed later?
Yes — they are stored as objects alongside the page rather than as part of it, so they can be deleted individually or stripped entirely. Flattening is what makes an annotation permanent page content.
How do I invert a PDF for night reading?
That is a viewer setting rather than a change to the file. Acrobat offers it under accessibility preferences and macOS has a system-wide Smart Invert. The document itself is untouched.