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I have a pdf file and want to mask some sensitive information in it such as social security numbers. Can this be done, without having to use paid tools? Better yet, without having to download anything?

morpheus
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2 Answers2

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Source: I worked at a major multinational law firm as tech support.

If security is your goal and you need to complete erase any chance of the redacted information being retrieved, the only valid way to process any document for this goal is to either:

A. Black out the text and then print it.

-or-

B. Print the text and then black it out using a black marker.

-then-

Scan the blacked out document back into digital format, inspecting the document to confirm the scanned images will not reveal the hidden text through adjustments in color or contrast or brightness.

Any other method leaves the chance that metadata or other embedded information may still contain the redacted information.

Only by converting to an entirely non-digital media (physical print) and then back will you end up with a digital file guaranteed to be free of any chance the redacted information is still attached to the document somehow.

Community
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music2myear
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    Absolutely right. Can't believe it took almost 7 years before this got posted. It's a good thing a spammer brought this thread to people's attention. Who says that spam isn't useful? – fixer1234 Jan 25 '19 at 22:56
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You could open it with gimp, paint over the sensitive information and then print/save to pdf again.

Or do the same thing with inkscape - however as mentioned in the comments this is less safe as the information may still be present in the saved file (even if you can't see it on the pdf).

Both are free tools and available on a variety of platforms.

More pdf editing options are covered in this question

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jmetz
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    Be very careful, depending on the tool, redaction may or may not be complete. Some of the PDF editing tools that offer redaction do cover up the information, but they do it in a layered fashion. So if you open the file in an editor again, even though you cannot see the redacted text, you can use the text selection tool to copy the text to the clipboard. – EBGreen Jul 26 '12 at 19:36
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    @EBGreen- Good point - from that point of view gimp would be preferred as the text is transformed into an image first, avoiding that caveat. – jmetz Jul 26 '12 at 19:42
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    @EBGreen Haha, I remember opening files with redacted text on a slow computer many years ago...you could briefly see the redacted text before the black bars were rendered. – rob Nov 23 '13 at 18:25
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    There was a scandal in Britain when somebody in a government department 'redacted' a sensitive MS Word document by highlighting in black all the text that they wanted to 'hide'. I think they said it 'identified a training need'. – Michael Harvey Jan 25 '19 at 18:29