# Redact PDF — Technical Tool Documentation > **Summary:** Draw black rectangles over sensitive areas and export a flattened PDF. > **Tool Route:** `/tools/redact.html` > **Visual Guide Route:** `/guides/redact-pdf/` > **Category:** Secure PDF > **Processing Architecture:** 100% Client-Side. Zero server uploads. --- ## 1. What the Tool Does Redact PDF renders pages for marking, then draws black rectangles into the output PDF. Inspect the exported copy carefully before sharing. **Requirements & Constraints:** One readable PDF is required. Redaction coordinates are based on the rendered page and must cover the complete sensitive area. --- ## 2. When to Use It Use **Redact PDF** whenever you need to perform client-side secure pdf operations without uploading confidential records to third-party cloud servers. **Ideal Scenarios:** - Working on personal identity records, banking statements, medical filings, or NDAs requiring 100% local confidentiality. - Fast offline or low-bandwidth processing directly in your web browser. - Universal cross-platform document operations on Windows, macOS, Linux, Android, or iOS. --- ## 3. Key Implemented Features - **Engine Architecture:** `pdf.js (preview) + pdf-lib (page.drawRectangle with black fill)` - **Zero Server Uploads:** Processing executes directly within client browser memory. - **Instant Processing:** Fast execution powered by WebAssembly and native HTML5 APIs. - **Review Previews:** Visual feedback and progress indicators confirm results prior to saving. - **No Sign-up / No Watermarks:** Full functionality with zero paywalls or forced branding. --- ## 4. Supported Input Files - **Primary Input:** Single PDF document (.pdf) - **Validation:** Files are validated in the browser prior to parsing. --- ## 5. Supported Output Files - **Output Format:** Permanently redacted PDF document (redacted.pdf) - **MIME Types:** `application/pdf` (or appropriate image/text/zip formats). --- ## 6. File Size & Memory Limits - **Recommended Bounds:** Client RAM bound - **Technical Context:** Modern browser tabs enforce memory quotas (typically 1.5 GB to 2 GB per tab). PDFHub handles documents comfortably within standard browser memory limits. For files exceeding 150 MB or 1,000 pages, splitting into smaller sections is recommended. --- ## 7. Step-by-Step Instructions 1. **Upload a PDF and choose a page.** 2. **Drag over every sensitive region to create a black box.** 3. **Move through pages and repeat as needed; use Clear Page to start a page again.** 4. **Select Save Redacted PDF and verify the result in a separate viewer.** --- ## 8. Required User Inputs & Controls - **File Upload Area (`#drop` / `#fin`):** Click to open native file browser or drag and drop supported files. - **Tool Options (`#opts`):** Dynamic settings panel configuring parameters, page ranges, or compression levels. - **Execution Button (`Save Redacted PDF (#goBtn)`):** Triggers client-side processing pipeline. - **Reset Button:** Clears loaded files and resets workspace to pristine state. --- ## 9. Processing Behavior & Execution Pipeline Renders page previews, captures user-drawn bounding boxes over sensitive regions, translates coordinates to PDF coordinate space, draws opaque black rectangles permanently onto the page content stream, and saves. --- ## 10. Expected Output & Download Verification - Upon successful execution, the interface triggers an automated browser download via `downloadBlob()` or opens a result review modal. - Users can verify file size, page count, and visual rendering before finalizing the download. --- ## 11. Practical Example Use Case Blacking out Social Security Numbers, credit card details, or confidential client names before public disclosure. --- ## 12. Common Errors & Troubleshooting - **Issue:** If a box is misplaced, clear that page and redraw. - **Issue:** If text can still be selected outside a box, expand the redaction area and export again. - **Avoid:** Redacting only a screenshot layer or forgetting another page. - **Avoid:** Sharing the source PDF instead of the redacted output. - **Tip:** Assuming transparent highlights redact text. Redact tool draws solid 100% opaque black rectangles. --- ## 13. Privacy & Data Handling Architecture - **Local Processing:** 100% Client-Side. Zero server uploads. - **Browser Memory:** Document bytes reside temporarily in `ArrayBuffer` memory and are garbage collected when the browser tab is refreshed or closed. - **Cookies & Telemetry:** PDFHub sets zero tracking cookies, zero analytics beacons, and stores zero personal document data. --- ## 14. Frequently Asked Questions (FAQ) #### Q: Is redaction reversible? **A:** Treat the exported result as permanent, but retain the source privately. #### Q: Does it detect sensitive text automatically? **A:** No, marking is manual. --- ## 15. Related PDFHub Tools - [Protect PDF Documentation](protect-pdf.md) - [Edit PDF Documentation](edit-pdf.md) - [PDF Forms Documentation](forms-pdf.md) --- ## 16. Links & Resources - **Launch Live Tool:** [Open Redact PDF in PDFHub](../../tools/redact.html) - **Visual Tutorial:** [View Redact PDF Visual Guide](../../guides/redact-pdf/) - **All Tools Master Reference:** [All Tools Reference](../all-tools-reference.md) - **Master Documentation Index:** [Documentation Index](../documentation-index.md) --- ## 17. Visual Walkthrough & Interface Screenshots ### Step 1: Open Redact PDF - **Interface Control:** `Upload Drop Zone (#drop)` - **What You See:** The drop area accepts any PDF document containing confidential information. - **What to Do:** Open Redact PDF to permanently black out and sanitize private, personal, or financial data. - **Practical Pro-Tip:** Redaction permanently deletes the underlying text and vectors, preventing data recovery. ![Redact PDF Step 1 - Open Redact PDF](../images/redact-pdf-step-1.png) ### Step 2: Upload Sensitive PDF - **Interface Control:** `File Browser (#fin)` - **What You See:** The document renders in the interactive redaction canvas viewer. - **What to Do:** Select your confidential PDF file from your storage. - **Practical Pro-Tip:** Redaction is irreversible; keep an unmodified backup of your original file. ![Redact PDF Step 2 - Upload Sensitive PDF](../images/redact-pdf-step-2.png) ### Step 3: Select Target Page - **Interface Control:** `Page Switcher (changePage)` - **What You See:** The canvas viewer displays the active page with full document legibility. - **What to Do:** Navigate to the exact page where confidential text or numbers appear. - **Practical Pro-Tip:** You can redact multiple pages across the document in one session. ![Redact PDF Step 3 - Select Target Page](../images/redact-pdf-step-3.png) ### Step 4: Draw Blackout Redaction Box - **Interface Control:** `Redaction Canvas (#editor, canvas)` - **What You See:** An opaque solid black box covers the confidential content entirely. - **What to Do:** Click and drag a blackout rectangle directly over the private text. - **Practical Pro-Tip:** Drag slightly past the edges of sensitive text to ensure full coverage. ![Redact PDF Step 4 - Draw Blackout Redaction Box](../images/redact-pdf-step-4.png) ### Step 5: Inspect Redaction Coverage - **Interface Control:** `Blackout Overlay Preview` - **What You See:** Solid blackout blocks conceal all private numbers and names completely. - **What to Do:** Review the drawn blackout boxes to confirm nothing sensitive is exposed. - **Practical Pro-Tip:** Check headers and footnotes for repeated account numbers or IDs. ![Redact PDF Step 5 - Inspect Redaction Coverage](../images/redact-pdf-step-4.png) ### Step 6: Click Save Redacted PDF - **Interface Control:** `Save Action Button (button.btn-primary)` - **What You See:** The redaction engine removes the underlying text stream and bakes solid black vectors. - **What to Do:** Click the primary "Save Redacted PDF" button. - **Practical Pro-Tip:** Text beneath redaction boxes cannot be highlighted, searched, or extracted by any tool. ![Redact PDF Step 6 - Click Save Redacted PDF](../images/redact-pdf-step-4.png) ### Step 7: Download Sanitized PDF - **Interface Control:** `Download Dialog (#dlModal .btn-success)` - **What You See:** The download modal confirms your redacted document is safe for public release. - **What to Do:** Click "Download" to save your permanently sanitized PDF. - **Practical Pro-Tip:** Your sanitized document is now legally safe for public filings or third-party audits. ![Redact PDF Step 7 - Download Sanitized PDF](../images/redact-pdf-step-4.png)