Black Box on a PDF Doesn’t Hide the Text

How do I fix it?

Open the file in Redact PDF Drag boxes over everything that must go. Redaction removes the characters inside each box and draws the black area in their place.

Check every page, not just the obvious one The same number usually appears in a header, a reference line and the covering letter. Thumbnails make it quick to walk the whole document.

Save, then try to copy from the result Select across the redacted area in the saved file and paste. Nothing coming out is the proof that the words are gone.

Clear the metadata before sending Redaction handles the page; author names and editing dates sit elsewhere in the file and travel with it.

Why does this happen?

Text and graphics are separate layers. A PDF stores characters and drawings independently. Painting over one does not change the other, however opaque it looks on screen.
Highlighting and marker tools are annotations. A black highlight is an annotation floating above the page — it can be selected, moved or deleted by the person who receives the file.
Exporting to PDF does not merge the layers. Covering text in Word and exporting keeps both objects. The box is a shape, and the text is still text.
Screenshots hide the text but lose everything else. Taking a picture of the page does remove the text layer — along with the ability to search, select or reuse any of the rest of it.

Questions

Can someone really recover text under a black box?

Yes, by selecting the area and pasting it, or by running any text extractor over the file. It has caused real disclosure incidents in court filings and corporate reports.

Does flattening the PDF make the box safe?

It makes the box permanent, but the text underneath is still in the page content and still extractable. Redact first, then flatten if you want.

What about a scanned page?

A scan has no text layer, so a box over it does hide the pixels. Flatten the file so the box cannot be dragged away by the recipient.