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What methods are there to blackout a part of a PDF?

I don't want to simply use Preview's annotation tools and then save the document, since then someone could open up the PDF and remove the annotation to reveal the part of the document which I'm trying to black out.

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12 Answers 12

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If you want to leave it as a PDF, you really need to use the actual redaction tools in Adobe Acrobat, otherwise you are simply leaving yourself open to reversals.

https://www.adobe.com/acrobat/resources/how-to-redact-a-pdf.html

If you want to save the PDF as a graphics file, then any black box over the words should work.

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128

If you are looking for a no-cost way in Preview.app

  1. File->Export (or save as)
  2. Export PDF to TIFF file format (it's a multipage image format)
  3. Open TIFF file
  4. Export TIFF to PDF file format

Maintains page structure, OCR will be lost.

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  • 7
    This method was truly the best approach for me. No software installs necessary.
    – Sonny
    Commented Sep 10, 2014 at 14:36
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    Would you care to comment how the feature of being able to go back to the previous version of a document comes into play here?
    – cnst
    Commented Sep 20, 2014 at 0:29
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    @cnst: I think the idea is to create a redacted copy, and leave the original PDF alone.
    – mklement0
    Commented Feb 17, 2015 at 17:38
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    Great solution. Note that in cases where using the TIFF document directly is acceptable, it's worth turning on compression for the TIFF export (e.g., LZW works on Windows, too), so as to prevent the file from becoming much larger than the original. (If you convert back to PDF, this is not necessary, because the conversion apparently applies compression implicitly).
    – mklement0
    Commented Feb 17, 2015 at 17:42
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    Try "Paintbrush" for OSX for a solid, free mspaint-like program to do the manual redacting.
    – Sean Glover
    Commented Jan 28, 2016 at 22:35
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A free solution, is to convert the PDF to an image, then save it as a PDF again. The only drawback is that the PDF will remove any OCR info it might have had.

Steps:

  1. Open the PDF file to redact in Preview.
  2. Black out text using any method you want (e.g. use the rectangle annotation tool with black as the color and choose the thickest border. Then draw the shape as many times as needed until your document is blacked out.)
  3. File > Save As, and choose an image format such as PNG or GIF.
  4. Open the saved image file, then File > Save As, and choose PDF.
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  • wow that's a painful brute force approach.
    – WestCoastProjects
    Commented Feb 6, 2016 at 1:34
  • This is a better approach than the current leader, because it not only removes OCR, it blacks out stuff too.
    – jvriesem
    Commented Nov 20, 2018 at 5:00
  • GIF is probably not the best option for this sort of thing
    – ma1234
    Commented Mar 5, 2023 at 2:03
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Big Sur’s Preview now has a Tools / Redact menu item that specifically deletes the content being redacted when the document is closed. More information in Apple’s Preview guide:

https://support.apple.com/guide/preview/annotate-a-pdf-prvw11580/11.0/mac/11.0

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PDFPen has a redaction tool which works properly.

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    Beware though, of information in graphical, rather than textual form: This is harder to redact.
    – Harald Hanche-Olsen
    Commented Aug 21, 2011 at 15:31
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    I believe that my original answer would work properly for graphical data.
    – Senseful
    Commented Aug 23, 2011 at 6:47
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    @Senseful: No. I just tried it. The result is here. You can't tell by looking, but the file contains three images, layered atop each other: At the bottom the original images, and on top of that, the annotation rectangle and its border as two separate images. The pdfimages tool (comes with poppler, which I have via MacPorts) extracts all three images, letting me read the not-so-secret secret.
    – Harald Hanche-Olsen
    Commented Aug 23, 2011 at 20:19
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    Would saving the pdf as an image (eg GIF or PNG) in Preview, then saving that image as a PDF again properly redact graphical data? (ie, see apple.stackexchange.com/questions/22683/…) -- from my testing it seems to be a valid solution.
    – Senseful
    Commented Sep 3, 2011 at 17:51
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    @Senseful: Yes, that should work. However, in a multipage document, you would have to do that to every page, then reassemble the redacted pages afterwards. So it may not be the most practical solution, but I don't see any problems with it otherwise.
    – Harald Hanche-Olsen
    Commented Sep 6, 2011 at 19:42
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OK, so the only real solution is to redact a paper copy and then scan it back in!

All other methods mentioned here don't work properly.

Importing the image in to GIMP and editing it there doesn't work, as once the page is put back in to a PDF document, that page is no longer text searchable as the whole page is now seen as an image!

Skim just doesn't work for redacting text. Or maybe it's just completely unintuitive with no good help.

Most other methods leave the text accessible beneath the redacted 'white outs'.

I have given feedback to Apple about this (http://www.apple.com/feedback/macosx.html)

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I opened the PDF in preview, exported it as a jpg. Opened word/pages and pasted the jpg into the document and then used a rectangle box to blackout whatever I wanted to and then I exported it as a pdf.

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ScanTango

Features include redaction.

Using a demo version today: the option to redact is greyed out, so I can't confirm its efficacy.

According to a 2008 post by Adam Greivell:

… the redaction tool worked pretty well. Actually, it even seemed to muck up the text in a live pdf document so you couldn’t copy what was under the redaction. … I can’t say how much I’d trust this feature with sensitive live text. I scanned all of my documents to PDF with no OCR before I did my redaction. Then, I printed to PDF to add one more layer of separation to make sure nobody could see what was behind the redactions.

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I tried saving my image as an image in preview and this only works if your pdf is one page. If it's multiple pages, exporting as an image will only save the first page.

The solution I found was this (it's a bit tedious, but you can get through it pretty fast once you get the hang of it):

Open PDF in GIMP (free photo editor) as an image. Only open those pages that need redaction. When you open it as an image, it essentially flattens the pdf so you're no longer able to highlight and copy text.

Use tools in GIMP to black out text.

Then, file -> print. On the print screen, choose "Print Preview". This will bring up the pdf in Preview where you can export/save the file.

If you have more than once page, then you can choose the thumbnail view in Preview and drag/drop the pdfs onto one another to form a larger document that you can then print. This is what I do when I have to sign just a few pages of a large pdf document.

Hope this helps!

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    As mentioned in the 'no-cost way' above you need to export as a TIFF which supports multiple page output.
    – Pierz
    Commented Aug 11, 2015 at 8:59
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Open your PDF or image.

Use the line tool or whatever to make your redactions.

Then File>Print. Instead of printing to paper, save it as a PDF. Doing it this way causes the black lines or boxes to no longer be clickable. If you just "save as" a new PDF, the boxes remain able to be manipulated,

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    Sadly, this approach has one fatal flaw: if you redacted by simply placing opaque boxes over the content of interest, you can still select and copy & paste the obscured content; also, hyperlinks in the obscured content continue to work, too.
    – mklement0
    Commented Feb 17, 2015 at 17:02
  • And if you disable copy paste without a password you can use the find tool to guess the text underneath. It takes time and trial and error but account numbers have a limited symbol space
    – boatcoder
    Commented Jan 31, 2020 at 15:00
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PDF Studio version 8 has a manual redaction tool built-in its content editing tool. It is real redaction that actually removes content. It can select text and images in the PDF document content and redact them.

PDF Studio version 9 (coming March 2014) will have a full fledged redaction feature where users can select an area on a document, and it will redact any images or text intersecting with this area.

PDF Studio works on Mac (including 10.9 Mavericks) but also Windows and Linux and the same license key can be used on 2 different computers with different OS.

http://www.qoppa.com/pdfstudio/

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The subject of redation of PDF files seems to be a difficult subject concerning programming. As Acrobat Pro CD is much to expensive for me as a private non-profit user, I was looking for an alternativ. It took me rather long time to find a real good alternative to Acrobat Pro:

  • PDF Studio PRO from Qoppa (http://www.qoppa.com/pdfstudio/): This tool really gives you virtually the whole functionality of Acrobat Pro. It is a solid part of software and according to my extensive tests the only tool that is really able to redact safely PDF files. Note that you need the PRO version, as the standard version lacks the ability of redaction.

I tried several other possibilities, which all don't work properly:

  • Apple Preview: this application allows to visually hide parts of a pdf behind a box, but it is always possible to remove the box or copy / paste the text behind as the sensitive information is NOT removed from the file!

  • PDF Pen: PDF Pen seems to be a nice tool and it offers a nice reaction functionality - seems to at least. Be careful about this tool: it messes up your PDFs completely as you redact. Therefore the functionality is limited to a files who are by chance compatible with this tool. Especially in PDFs with pictures (i.e. all scanned files) PDF Pen has big problems and messes up your file so it gets irreversibly unusable. My contact with the support never brought a solution so far over a time of several weeks.

  • Nuance PDF Coneverter for Mac: I bougth this tool as it offers a redaction functionality. Unfortunately there is no trial version available, but the refunding worked fine without problems. As soon as I had the tool installed, I had to realise, that it was nothing else than PDF Pen under a different hood. Now you don't have to wonder, why PDF Pen is using the OCR engine of Nuance :-). For the record: PDF Pen = Nuance PDF Converter for Mac. Same errors while redacting as expected. Result: equally useless as PDF Pen.

As a simple summary I suggest you spend the $129 for PDF Studio PRO from Qoppa.

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  • I have had excellent support from PDF Pen. Years of it in fact. I can't speak for the product here, but I would encourage anyone to test drive PDF pen for free before paying for anything other than Preview app.
    – bmike ♦
    Commented May 15, 2016 at 21:53

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