Why a black box is not proof of permanent redaction
By PDFEditor.ae · Published
The problem with black boxes
In many PDF tools, drawing a black rectangle adds a shape on top of the page. The text underneath is still in the file: anyone can select it, copy it, search for it or delete the rectangle. Documents have been published with "redacted" names that could be read by copying the hidden text.
What real redaction does
Redaction removes the content from the file, not just from view. In our editor, the Redact tool marks an area; when you download, every page with a redaction is turned into an image with the area filled in black, and the original page content is discarded. We test this by redacting a known word in a sample file and confirming the word cannot be found anywhere in the downloaded file, including inside its compressed data.
Trade-offs of our method
- The rest of the text on a redacted page also becomes part of the image, so it is no longer selectable or searchable.
- Links on that page stop working.
- Pages without redactions are not affected.
How to check any redacted PDF
- Open the downloaded file and try to select text under the black area.
- Search (Ctrl+F) for a word you redacted.
- Copy the whole page and paste it into a text editor.
- If the redacted words appear in any of these, the redaction failed — do not send the file.
Also check
Redaction covers what is on the page. Before sharing a sensitive document, also consider the file name, any earlier versions you sent, and attachments that repeat the same information.