Black boxes in PDFs often hide text rather than delete it, experts warn

A common redaction mistake involves drawing a black rectangle over sensitive text in a PDF instead of actually removing the underlying data. Because both methods look identical on screen, the error frequently goes undetected before documents are filed in court or released under FOIA requests. The text remains fully extractable using basic tools such as pdftotext, which will display the supposedly hidden content in plain form. The flaw stems from how PDF content streams work: if the text operator appears before the fill rectangle operator, the name is painted first and then covered, leaving it intact in the file. Proper redaction requires using a dedicated redaction tool and explicitly applying the marks so the text is permanently removed, not merely obscured.