Why a black box is not enough
A PDF stores the text and, separately, whatever is drawn on top of it. A black box, a black highlight, or a shape added with a regular editor is just one more drawing: the text underneath is still in the file. That is why it can be selected and copied, found with Ctrl+F, read by a screen reader, or “unredacted” by moving or deleting the box.
How to check whether a PDF is properly redacted
- Select all the text (Ctrl+A), copy it, and paste it into a text editor: if the redacted text shows up, it was not removed.
- Search with Ctrl+F for a name that should be redacted.
- Open the file properties and look at the author, title, and subject.
- Check the comments panel and the layers panel.
What else needs cleaning
- Metadata: author, title, subject, application, and dates.
- Comments and annotations: they often contain names, and the names of whoever wrote them.
- Hidden layers and objects outside the page.
- Bookmarks, form fields, and attachments.
- The text layer of a scan: if the PDF went through text recognition, redacting the image does not remove the invisible text behind it.
Redacting without Adobe Pro
Redacting for real means removing the text, not covering it. Professional redaction tools do it in two steps: you mark and then you “apply”. If you do not have one, the rule is the same: the data must not stay in the file you share.
A safe approach is to work on the text: replace the data in the content and generate a new file.
How to do it with HILO
HILO reads the PDF’s text in your browser, automatically finds the names and personal data, and builds a new Word document with the text already replaced by codes. What was redacted does not remain in the new document. The PDF’s comments, annotations, and properties are not carried into the Word file, and a checker makes sure none of the replaced data was left.