Clean Scanned PDF
Scanned PDFs carry three problems: they are skewed, they have visual noise, and the text is an image you cannot search. Fixing them in the right order matters — enhance first, then OCR.
AI Scan Enhancer
Try it on a copy of your document — keep the original until you have checked the result.
AI Scan Enhancer
The three problems
- Skew: pages scanned at a slight angle. This hurts both reading and OCR accuracy.
- Noise: shadows from page curvature, speckle from compression, and bleed-through from the reverse side.
- No text layer: a scanned page is an image, so there is nothing to search, copy or extract until you run OCR.
Correct order
- Deskew and clean first. OCR on a skewed, noisy page produces more errors — fixing the image beforehand measurably improves recognition.
- Remove stamp or handwriting interference before OCR too: marks crossing text are a common source of misreads.
- Run OCR last, then spot-check numbers, dates and proper nouns.
What enhancement cannot do
- Enhancement works with the pixels present. It cannot recover detail a low-resolution scan never captured.
- If a document is important and the scan is poor, rescan at higher DPI rather than trying to repair it — usually 300 DPI for documents, more for small print or stamps.
After OCR
- Verify by searching for a phrase you can see on the page. If search fails, the text layer did not render.
- Check figures: OCR commonly confuses 0/O, 1/l and 5/S. Always verify amounts and identifiers.
Caution: Enhancement cannot restore detail that was never captured. For poor originals, rescan at higher resolution instead of repairing.
Step by step
- Deskew and clean the scan (shadows, speckle).
- Remove stamp or handwriting marks that cross text.
- Run OCR with the correct language.
- Search for a visible phrase to confirm the text layer works.
- Verify numbers and identifiers manually.
PDFnoted product team · Published 2026-09-02
Based on how PDF annotation objects, page content streams and document metadata are defined in the PDF specification, and on the behaviour of PDFnoted’s own tools. Reviewed periodically.
General guidance for document handling only; not legal advice. Where a document may be used as evidence, keep an unmodified original and consult a qualified professional.
FAQ
- How do I clean up a scanned PDF?
- Deskew the pages, reduce shadows and speckle, then run OCR to add a searchable text layer. Doing enhancement before OCR materially improves accuracy.
- Should I OCR before or after cleaning?
- After. OCR performs better on straight, clean images, so deskew and denoise first.
- What resolution should I scan at?
- Around 300 DPI suits most documents. Use more for small print, stamps or fine detail.
- Can cleaning fix a blurry scan?
- Only partly. Enhancement works with existing pixels; it cannot recover detail a low-resolution scan never captured. Rescan instead.
- Why does my OCR output contain errors?
- Usually skew, noise, low resolution, or marks crossing the text. Clean first, then re-run OCR and verify figures.
- How do I know the text layer worked?
- Search for a phrase visible on the page. If search returns nothing, the text layer is missing or failed.
- Does OCR change how the page looks?
- No. It adds an invisible text layer beneath the image; the appearance is unchanged.
- Is it safe to upload scanned documents?
- Use a browser-local tool for anything confidential so the file never leaves your device.