How this works in your browser
Tesseract, the long-established open-source OCR engine, is compiled to WebAssembly and loaded into your browser tab along with the trained data for the language you choose. Each PDF page is rendered to a canvas image through PDF.js and handed to the engine, which segments the image into lines and characters and matches the shapes against its model to produce text plus the coordinates where it found each word. Those coordinates are what make a searchable PDF possible: the recognised text is written back over the original scan as an invisible layer positioned exactly on top of the visible words, so the page looks untouched while becoming selectable and searchable. All of it runs locally, which is why it is slower than a server service but never exposes the document.
OCR PDF vs. traditional online converters
| Feature | OCR PDF (in-browser) | Traditional online converters |
|---|---|---|
| File upload required | No - never leaves your device | Yes - file is sent to a server |
| Processing queue | None - starts instantly | Often, especially at peak times |
| Watermark on output | Never | Common on free plans |
| Usage limits | None - free, unlimited use | Often capped per day or file size |
| Works offline once loaded | Yes, for most tools | No - requires a live connection |
| Account required | No | Often, for anything beyond a trial |
How to use OCR PDF
- 1
Open the OCR PDF tool
Go to tools.slaytic.com and open the OCR tool. No sign-up or account required.
- 2
Drop your scanned PDF and pick a language
Add the file and select the language of the document, which meaningfully improves accuracy compared to leaving it on a default.
- 3
Run OCR and download
Let each page be processed, then download either a searchable PDF with an invisible text layer or the extracted plain text.
Common ways to use OCR PDF
Making an archive searchable
Turn a folder of scanned contracts, invoices or records into documents you can actually search by keyword.
Extracting text from a photographed page
Pull usable text out of a document you captured with a phone camera rather than retyping it.
Meeting accessibility requirements
Add a real text layer so screen readers can read a document that was previously just an image of a page.
Frequently asked questions
Which languages does the OCR support?
English, French, German, Spanish, Italian, Portuguese, Arabic, Russian, Chinese (Simplified), and Japanese. Select your language before running for best accuracy.
My PDF already has selectable text - do I need OCR?
No. OCR is only for scanned or image-based PDFs where the text is a photo, not real characters. If you can already highlight text in your PDF reader, OCR is not needed.
How accurate is the OCR?
Accuracy depends on scan quality, font clarity, and language complexity. Clean, high-resolution scans of printed text typically achieve 95%+ accuracy. Handwriting, decorative fonts, and low-resolution scans will be less accurate.
Why is OCR so much slower than the other tools?
Because it is doing genuinely harder work. Most tools here restructure data that already exists; OCR runs a recognition model over every pixel of every page to work out which shapes are letters. That is computationally heavy, and it runs on your device rather than a server farm, so expect seconds per page rather than instant results.
Does the page still look the same afterwards?
Yes. The recognised text is added as an invisible layer sitting exactly over the words in the scan. Visually nothing changes, but you can now select, copy and search the text, and a screen reader can read it.
How can I improve the results?
Scan quality matters far more than any setting. Aim for 300 DPI or better, get the page square rather than skewed, use good even lighting if photographing, and pick the correct language before running so the engine uses the right character set.
Is my document uploaded for processing?
No. Tesseract runs as WebAssembly inside your browser tab, which is unusual for OCR since most services require an upload. Sensitive scans never leave your device.