Redaction module

The Redaction module lets you permanently hide confidential passages in a document before distributing it: names, addresses, personal data, amounts, internal references, and so on. It is designed for contexts where simply overlaying an image is not enough (transmission to a third party, legal anonymisation, publication online, and so on), because it offers irreversible removal of the underlying content. You reach this module from the Editing category of the Dashboard.

Difference from a highlight or a rectangle

A redaction differs from a simple annotation (a black rectangle or a highlight) in that it physically removes the content under the mask once confirmed. A black rectangle placed over text can be worked around: by selecting the area or exporting the PDF as text, the hidden content can be recovered. With permanent redaction, the text and graphic elements under the mask are erased and replaced by an opaque colored rectangle.

Step 1 — Preparing the areas to redact

The process runs in two stages: first you define redaction rectangles (areas to mask), which stay editable as long as you have not confirmed; then you apply the removal permanently.

Choosing the masking color

The sidebar offers three standard fill colors:

Black (default) — the most common option for masking text;
White — useful for passages in areas with a white background, where the mark must stay invisible once printed;
Grey — for documents needing a less pronounced contrast.

The outline of the redaction rectangles stays red during editing so you can identify them clearly, whatever fill color you chose.

Selecting the text to mask

In the PDF view on the left, select text by dragging the cursor;
In the sidebar, click Mask selection.

HtkPDF draws a redaction rectangle over the location of the selected text. You can repeat the operation as many times as needed to prepare several areas to redact, on the current page or on the other pages of the document.

The Mask selection button is disabled as long as no text is selected.

Note: at this stage, the rectangles are ordinary annotations. You can move them, resize them or delete them (Delete key) as long as you have not applied the redaction.

Step 2 — Applying permanently

Once all your redaction areas are prepared and checked, click the Apply permanently button. HtkPDF then rewrites the document asking PDFKit to burn in the annotations (burnInAnnotations): the system engine applies each redaction rectangle and removes the content it covers — text and graphics alike — before replacing it with the chosen colour.

The operation is irreversible once saved: it is no longer possible to recover the content under the mask, not by selecting the PDF, not by exporting it as text, and not by converting the document. That is precisely what distinguishes redaction from a simple annotation.

Confirming and history

Until you have clicked Apply permanently, the redaction rectangles are saved as ordinary annotations and appear in the document History. Applying permanently also creates a checkpoint, but once the document has been saved, that checkpoint no longer allows the erased content to be recovered: only the post-redaction visual rendering is kept.

Like every editing operation, redaction goes through the pending changes state until the document is explicitly saved through the Save button on the Dashboard (⌘S).

Best practices

Always keep an archive copy of the original document before applying the redaction, in a secure folder. Once the permanent redaction has been saved, there is no way back.
Check every rectangle before clicking Apply permanently. A missed area will leave the content visible in the distributed document.
Do not forget the metadata: a name redacted in the body of the document may survive in the PDF attributes (author, keywords, subject) or in the OCR layers. Always combine redaction with the Scrub metadata module before distributing a sensitive document.
Beware of scanned PDFs: on an image document without a text layer, text selection is not possible; you can nevertheless prepare redaction rectangles by hand using the Shape annotations (black rectangle) and then apply Flattening, but those areas are not covered by this module's permanent redaction mechanism.

Screenshots

1 screenshot — click to enlarge