How to Redact a Scanned PDF

To redact a scanned PDF, you must first run optical character recognition (OCR) to convert the image-based content into searchable text. Without OCR, the PDF is a stack of image pages and no tool can detect or remove text from it. After OCR, apply permanent redaction using a tool that modifies the PDF content stream and removes both the image regions and the underlying text layer.

Why scanned PDFs need OCR first

A scanned PDF is technically a series of images wrapped in PDF format. There is no text layer to redact. Until OCR is applied, search tools find nothing, AI PII detection finds nothing, and your only redaction option is manually drawing black boxes on the image, which leaves the underlying image data intact unless the redaction tool also flattens or replaces the pixels.

The right scanned-PDF redaction workflow

1. Run OCR. Adobe Acrobat Pro has Tools > Recognize Text, which writes a text layer underneath the scanned image. Open-source ocrmypdf does the same. Dedicated redaction tools like RedactifyAI run OCR automatically as part of the upload step.
2. Use AI or manual review to mark sensitive content in the OCR'd text layer.
3. Apply permanent redaction. The tool should both delete the text from the OCR layer and replace the corresponding image pixels with a solid block. Tools that only delete the text layer leave the image content readable.
4. Save as a new file and verify by trying to copy text from the redacted areas and by checking that the redacted regions appear as solid blocks in any PDF viewer.

What can go wrong

OCR errors can cause PII to be missed if a Social Security number is misread or a name is split across two text boxes. Always have a human review the AI-detected redactions on a scanned document before applying. The image-pixel-replacement step is also where many cheap tools fail, they remove the text layer but leave the image, so the redacted region looks fine on screen but extracts cleanly when re-OCR'd by an opposing party.

Try it free: RedactifyAI runs OCR automatically on scanned PDFs and applies permanent redaction to both the text layer and the image. Try it at redactifyai.com. Free tier available, no card required.