PDF redaction vs a black box: what changes inside the file?

Two PDFs can look identical while retaining different information. One may contain original text covered by a shape; the other may contain only a new image in which that region has been replaced.

What an overlay does

A PDF can store text, images and drawing instructions as separate objects. Adding an opaque rectangle changes the visible result without necessarily deleting the objects below it. Copying text, extracting page content or editing the PDF may still reveal those objects.

What CloakDoc’s two exports do

The manual viewer currently loads the original PDF and draws rectangles onto its pages. It clears some descriptive fields, but the underlying content remains. Treat this output as a visual markup, not a confidential distribution copy.

The batch workflow renders a page, fills detected regions in the pixels, then embeds the resulting image in a new PDF. Original text objects and attachments are not copied. This removes covered source content from that export, while preserving anything still visible outside the covered regions.

Understand the tradeoff

Rebuilding pages from images loses selectable source text, interactive forms and other structure. Fine detail and file size can change. It also does not protect against missed identifiers or sensitive details that the matching rules were never designed to recognize.

Check more than appearance

Reopen the exported file in a separate reader. Search for a known covered value and try selecting text. Check document properties and attachments. A failed search is not sufficient proof: a sensitive value can still be visible as pixels, or use an encoding your search did not find.

Choose based on the required result

Use overlays when reviewing which areas need attention. For disclosure, use a removal workflow appropriate to all required regions and verify the final output. Do not infer removal from a button label, a black rectangle or a filename containing “redacted”.