How to Run OCR on a PDF Without Uploading It to Any Server

Why OCR on Scanned Documents Is a Privacy Problem

A scanned document is essentially a photograph of text. To make it searchable, you need OCR — software that reads the image and identifies characters.

The catch: OCR is computationally heavy. Until recently, doing it in a browser was impractical, which meant every OCR service required a server upload. Your scanned contract, medical record, or financial statement would be transmitted to a remote server for processing.

This is no longer necessary.

Tesseract.js: OCR in the Browser

Tesseract is the world's most widely used open-source OCR engine, originally developed by HP and later made open-source. It supports 100+ languages and achieves high accuracy on typed documents.

Tesseract.js is a JavaScript port that runs Tesseract entirely in the browser via WebAssembly. FusioFiles integrates Tesseract.js for its PDF OCR tool.

The result: OCR that runs at near-native speed, entirely inside your browser tab, with no server involvement.

What OCR Actually Does to a PDF

A scanned PDF contains pages as image objects. OCR adds a text layer (invisible) underneath or above the image layer. The result is a "searchable PDF" — visually identical to the scan, but with a text layer you can:

• Search with Ctrl+F
• Select and copy
• Index in document management systems
• Process with downstream text extraction tools

The image layer is preserved. The document looks the same. It just becomes digitally functional.

How to OCR a Scanned PDF Without Uploading

1. Go to fusiofiles.com/ocr-pdf
2. Upload your scanned PDF — it loads into browser RAM only
3. Select the language of the document text
4. Click "Run OCR"
5. Download the searchable PDF

Processing time depends on the number of pages and your device's CPU. A 10-page document typically completes in 15–30 seconds on a modern laptop.

OCR Accuracy: What to Expect

| Document type | Expected accuracy | |---|---| | Clean, printed text (laser print) | 97–99% | | Printed text with some noise | 90–96% | | Typewriter text | 85–95% | | Handwritten text | 60–80% (varies greatly) | | Low-quality fax / photocopier | 75–90% |

For documents with poor scan quality, accuracy improves significantly with pre-processing: straightening skewed pages, increasing contrast, and removing noise.

Languages Supported

Tesseract.js supports 100+ languages including English, French, German, Spanish, Portuguese, Italian, Dutch, Arabic, Chinese (Simplified/Traditional), Japanese, Korean, Hindi, and many more.

For multilingual documents (e.g., a contract with both English and French sections), select multiple languages in the tool settings.

Extract text from your scanned PDF privately →