Adobe Acrobat’s redaction tool is excellent — and at $239.88 per year for a Pro subscription, it costs more than most people are willing to pay for an occasional task. If you just need to blur or black-box some sensitive information in a PDF before emailing it or posting it online, there’s no reason you should need to pay for that.

BlurPen is a free, browser-based tool that lets you redact any PDF in minutes — no Adobe, no account, no upload. Your file is processed entirely in your browser using open-source libraries (PDF.js and pdf-lib), and never sent to any server.

What PDF redaction actually means

There’s an important distinction worth understanding before you start: visual redaction vs. true redaction.

Visual redaction covers sensitive content on screen — with a blur, a pixelation effect, or a black box — but may leave the underlying text or data intact in the file. If you draw a black rectangle over text in a presentation tool and export it, someone can often remove that rectangle and read the original text.

True redaction permanently removes or replaces the underlying data so it can never be recovered, even with forensic tools.

BlurPen performs visual redaction at the pixel level using the HTML5 Canvas API. When you blur a region, those pixels are resampled or transformed — the original pixel values are gone. The resulting PDF is a flattened image of each page; there is no separate text layer that could be extracted. This is equivalent to scanning a paper document after physically obscuring the sensitive text.

For most use cases — sharing a screenshot of a bank statement, obscuring personal details before emailing a form, protecting a face in a document scan — this is exactly the right approach. For highly sensitive legal matters where provably irreversible redaction is required, consult a qualified attorney about appropriate tools and procedures.

How BlurPen handles PDFs (the quick technical explanation)

Understanding what’s happening under the hood helps you trust the result:

PDF.js (Mozilla’s open-source PDF renderer, self-hosted in BlurPen’s bundle) renders each page of your PDF into an HTML5 canvas element in your browser. No page content leaves your device at this step.
You apply blur or pixelation using the brush, rectangle, or ellipse tool. These effects are written directly to the canvas pixels using the Canvas 2D API.
When you export, pdf-lib (also self-hosted) takes each edited page canvas, converts it to a PNG image, and assembles all pages back into a clean, downloadable PDF. Again, nothing touches a server.

The key point: at no stage is your PDF uploaded anywhere. Everything runs locally in your tab.

Step-by-step: how to redact a PDF with BlurPen

Step 1: Open BlurPen

Go to blurpen.com/redact-pdf in Chrome, Firefox, Safari 16+, or Edge. No download, no account.

Step 2: Upload your PDF

Drag your PDF onto the upload zone or click to browse. Files up to 50 MB are supported. BlurPen will display the first page on the editing canvas. If your PDF has multiple pages, navigation controls appear below the canvas.

Step 3: Navigate to the right page

Use the ◀ Prev and Next ▶ buttons (or press ← / → on your keyboard) to move through the document. Each page loads on demand. You can return to any page and apply additional redactions — each page maintains its own edit history.

Step 4: Choose the right tool

Rectangle (R): Best for text blocks, form fields, addresses, or anything in a roughly rectangular area. Click and drag to define the box; the redaction fills it instantly on release.
Ellipse (E): Best for faces, profile photos, or rounded areas. Hold Shift while dragging to draw a perfect circle.
Brush (B): Best for irregular shapes — signature lines, hand-drawn annotations, or anything that doesn’t fit a geometric selection.

Step 5: Set blur or pixelation, and intensity

Toggle between Gaussian blur and Pixelation in the effect selector (or press G). For text and numbers — the most common redaction targets in PDFs — use Pixelation at High or Max intensity. This replaces the pixels with solid colour blocks, making the original data unrecoverable.

Set the Intensity slider to High or Max for anything sensitive.

Step 6: Apply redactions across all pages

Navigate through each page that contains sensitive content and apply redactions as needed. You can undo (Ctrl+Z / Cmd+Z) at any point within a page’s history.

Step 7: Export your redacted PDF

Click ⬇ Save in the toolbar and choose Save as PDF. BlurPen will compile all edited pages into a single PDF and trigger a download. The filename will have _blurred appended — for example, contract_blurred.pdf.

Frequently asked questions

Does it work on scanned PDFs? Yes. Because BlurPen operates at the rendered image level rather than the text layer, it makes no difference whether your PDF contains searchable text or is a pure scan. Both look identical to BlurPen — pixels on a canvas.

Is this GDPR-compliant? BlurPen processes your file entirely client-side with zero data transfer, so it doesn’t introduce any new data-sharing risk. Whether your redaction is sufficient for GDPR compliance depends on your specific situation — consult a data protection advisor for regulated contexts.

What if my PDF has 50 pages? BlurPen will warn you that large PDFs may render more slowly, but it will process the file. Pages are rendered individually as you navigate, so memory usage stays manageable. The 50 MB file size limit applies regardless of page count.

Can I redact the same region across multiple pages? Not automatically in v1 — you’ll need to redact each page individually. Batch preset application across pages is planned for BlurPen v2.

What format is the exported PDF? The exported PDF is a page-image PDF — each page is a flattened PNG image embedded in a PDF container. This is intentional: a flattened page has no text layer, metadata, or document structure that could leak redacted content.

Ready to try it? Open the PDF redaction tool — free, no account required →