LocalUtils field note · Mark and rasterize sensitive areas in a PDF
Mark and rasterize sensitive areas in a PDF
Drawing a black rectangle over text is not necessarily redaction. In many PDF editors, the original text remains under the rectangle and can still be copied, searched, or extracted.
This tool takes a destructive approach for pages that contain marks: it renders the page as an image, burns the black areas into those pixels, and places the flattened image on a fresh PDF page. Unmarked pages are copied rather than rasterized.
Quick start
- Add a PDF and wait for page previews to render.
- Open each page that contains sensitive material and draw boxes slightly beyond the full area that must disappear.
- Review every page at useful zoom, including headers, footers, repeated identifiers, attachments, comments, and pages with no marks.
- Export the rebuilt PDF, reopen it in another viewer, search for the removed text, and inspect document properties before sharing.
device → browser engine → result
What the browser does
PDF.js renders marked pages at approximately 2.5 times the page scale. The redaction rectangles are painted into the canvas. PDF-lib then creates a fresh page containing that raster image.
Rasterization removes the marked page's original selectable text and vector content from the exported page, but it also changes quality, accessibility, searchability, forms, links, and file size. Unmarked pages retain their original PDF content streams.
Inputs and outputs
- Input: a PDF that PDF.js can render.
- Marks: rectangular regions drawn on page previews.
- Output: a PDF with rasterized marked pages and copied unmarked pages.
Limits to know before you start
- The tool cannot know whether every sensitive area was marked.
- Unmarked pages are copied, so their original text, metadata, annotations, and attachments require separate review.
- Rasterized pages lose selectable text and may be less accessible.
- A visual black box can hide too little if the mark does not cover the complete glyph or surrounding context.
Troubleshooting
- If text appears outside a box, enlarge the mark and export again.
- If a page looks soft, compare the output at normal reading zoom; rasterization trades editability for destructive flattening.
- If the PDF contains forms, signatures, layers, or attachments, use a dedicated PDF security workflow and inspect those objects separately.
Verification checklist
- Search the exported PDF for every removed name, number, and phrase.
- Attempt to select or copy text from each rasterized page.
- Inspect metadata, attachments, comments, and unmarked pages independently; redaction marks do not clean them.
Questions people ask
Can the tool find sensitive text automatically?
No. The user chooses every rectangle. Detection and legal sufficiency remain the user's responsibility.
Is the result suitable for every legal disclosure?
No universal claim is possible. Requirements vary, and complex documents may need specialist review or approved redaction software.
Why are only marked pages flattened?
Copying unmarked pages preserves their quality and features, while marked pages are rebuilt to remove the covered source content.