How to mask sensitive information in a pdf file?

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?

2 Answers

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

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.