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PDF OCR

Turn scanned PDF pages into searchable documents. NoblePDF recognises the words on each page in your browser and adds a searchable text layer without replacing the original page image.

OCR

Choose a scanned PDF

Make image-based pages searchable and selectable.

or drop a PDF here

✓PDF stays on your device
✓Original page appearance preserved
✓Searchable PDF download
PDF
The OCR engine and selected language data may download when first used. Your PDF itself remains in the browser. OCR accuracy depends on scan quality, resolution, rotation and typography.
Preparing OCR…0%

Searchable PDF ready

Pages OCR'd-
Recognised words-
Output size-

Make scanned documents useful again

OCR converts text that exists only as pixels into a machine-readable text layer so you can search, copy and index scanned documents.

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Search scanned pages

Recognised words are added to the PDF as an invisible text layer while the original scan remains visible.

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Copy and find text

After OCR, compatible PDF readers can search and select recognised text that was previously just an image.

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Local-first processing

PDF rendering, recognition and PDF rebuilding happen in your browser. The OCR runtime may download code and language data.

How to OCR a PDF

1

Choose your PDF

Select a scanned or image-based PDF from your device.

2

Run OCR

Choose the document language and let NoblePDF recognise each required page.

3

Download

Save a new searchable copy while keeping the original page appearance.

How NoblePDF builds searchable text from scans

NoblePDF’s OCR workflow starts by rendering the PDF page with PDF.js and passing the resulting image data to Tesseract in the browser. The recognised words can then be represented as a text layer while the original visual page remains in place. This makes a scan searchable without requiring the page to be replaced by newly typeset text.

The current runtime bundles English, Spanish, French, German, Italian and Portuguese language data. Choosing the language that best matches the page can improve recognition, especially for accented characters and common word patterns. Mixed-language pages, handwriting, equations and stylised fonts remain more difficult.

Scanned-pages mode is useful when a PDF contains a mixture of real text pages and images. Re-running OCR over a page that already has a good text layer can create duplicate or misaligned text, so the tool can leave those pages alone. Use all-pages mode when there is a specific reason to replace or augment existing text.

OCR accuracy is not a legal or financial guarantee. Check names, dates, amounts and identifiers against the page image before relying on them. A clean-looking output can still contain substitutions such as 0/O, 1/l or punctuation mistakes.

Because recognition is CPU-intensive, long high-resolution scans can take significant time and memory. Splitting a very large scan into sections can improve reliability on mobile devices. The supported OCR path keeps the selected document and recognition work in the browser instead of uploading page images to a NoblePDF OCR service.

PDF OCR FAQ

Does NoblePDF upload my PDF for OCR?

For the supported OCR workflow, your PDF stays in the browser. PDF.js renders pages locally and Tesseract.js performs recognition in the browser. NoblePDF serves the OCR engine and supported language data from its own origin.

Will OCR change how the PDF looks?

The original PDF page content remains in place. NoblePDF adds an invisible text layer over recognised words rather than rasterising the document again.

Why can OCR make mistakes?

Recognition depends on scan resolution, blur, skew, handwriting, unusual fonts and language selection. Always review important extracted text.

What if my PDF already has selectable text?

The default Scanned pages only mode skips pages that already contain embedded text. Choose All pages only when you specifically want OCR applied everywhere.

Related NoblePDF tools

Compress PDFReduce the size of scanned PDFs.PDF ConverterConvert PDFs into Word, PowerPoint, images and text formats.Edit PDFOpen the full NoblePDF editor.

Improving an OCR result

Start with the best scan you have. OCR cannot invent detail that blur or compression destroyed. Straight pages, strong contrast and characters that occupy enough pixels are more valuable than simply increasing file size. If a phone photo is badly skewed, deskewing or rescanning can improve recognition more than repeatedly changing OCR settings.

Select the language that dominates the page. Names and numbers can still be recognised across models, but language data affects common character combinations and accented letters. For a multilingual document, process logical sections separately when accuracy matters and compare the result against the visible page.

Use search as a verification tool after OCR. Search the finished PDF for a few words from different pages, then copy and paste those words into a text editor to check ordering and character accuracy. If a page already had selectable text before OCR, compare it with the new layer to make sure duplicate text was not introduced.

OCR can support accessibility and discovery, but creating a high-quality accessible PDF can require more than invisible text. Correct reading order, tags, headings, table semantics and alternative text are separate document-structure tasks.

  • Review names, dates, dollar amounts and identification numbers manually.
  • Prefer scanned-pages mode when the document mixes scans and real text.
  • Split very large scans when browser memory is tight.
  • Keep the visual scan as the reference for anything the OCR result makes ambiguous.
Read the PDF structure first

OCR adds text recognition, not document semantics

Searchable OCR text is different from tagged accessibility structure and different again from native born-digital text. These pages explain the boundary.

Text PDFs vs image PDFs
What OCR can and cannot recover
Why OCR alone is not accessibility
Browse all PDF learning articles →