> Redacting a PDF robustly
How can I remove private material from a PDF document, so others can’t see it? Could I use Preview?
This is redaction, and it’s fraught with dangers which have led to the revelation of many secrets.
The rather naive approach of superimposing black boxes doesn’t work because others can easily remove them to reveal the underlying text. The PDF format is far from ideal in this respect, as it’s relatively simple to extract text from sections of a document which you think have been removed, as they’re retained in the file.
Preview now offers a simple redaction feature, but when tested it can easily leave hidden text behind, which you can’t see but can be recovered. Third–party PDF utilities offer improved reliability, but the only app to trust is Adobe Acrobat DC. Although, Acrobat DC is expensive and tricky to use.
Many simply print the document, redact it using marker pens, and scan it back in. Although time–consuming and tedious, this is the only way to guarantee that others can’t recover sensitive content.