1. What OCR actually does
OCR — optical character recognition — looks at the shapes in a scanned image and works out which letters and words they are. It then lays an invisible, selectable text layer directly over the picture. The page looks exactly the same, but now you can:
- Search the document with Ctrl/Cmd + F,
- Select and copy text into another app,
- and let it be indexed so it actually turns up in searches later.
2. Does your PDF need OCR? A 5-second test
Open the PDF and try to drag-select a line of text. If the words highlight, you already have real text — no OCR needed. If nothing highlights, or Ctrl + F finds no matches, the page is an image and OCR will make it searchable.
Rule of thumb: if you can't select it, you can't search it — and that's exactly what OCR fixes.
3. How to OCR a PDF for free
No software to install and nothing uploaded:
- Open the OCR PDF tool.
- Drop your scanned PDF into the box.
- Click to run OCR — each page is recognised right in your browser.
- Download the new, searchable PDF.
Make your scanned PDF searchable nowFree, in your browser — OCR runs locally, nothing is uploaded.
Open OCR PDF →4. Tips for accurate results
- Scan at 300 DPI. Crisp, high-resolution scans recognise far better than small or blurry ones.
- Keep pages straight. Skewed or rotated scans confuse OCR — straighten them first (you can fix orientation with Rotate PDF).
- Good contrast helps. Clean black text on a white background beats faint or shadowed photocopies.
- Pick the right language if the tool offers it, so accented and non-English characters come out correctly.
5. OCR vs. plain text extraction
These sound similar but solve different problems. If a PDF already has real text and you just want it pulled out into a .txt file, use PDF to Text or our extract-text guide — no OCR required. If the PDF is a scan (an image), you need OCR first to create the text in the first place. Just want the words from an image, not a new PDF? Image to Text reads a picture straight to text.
Explore the full free PDF toolkit28 tools that all run in your browser — no upload, no sign-up.
Explore PDFNest →Frequently asked questions
What does OCR do to a PDF?
It reads the text in a scanned image and adds an invisible, searchable text layer over the page. The PDF looks the same, but you can now select, copy and search the text.
How do I OCR a PDF for free?
Open a free OCR PDF tool, add your scanned PDF, and click convert. With PDFNest the pages are recognised in your browser and a searchable PDF is produced — nothing uploaded.
How can I tell if my PDF needs OCR?
Try to select a line of text. If nothing highlights, or Ctrl + F finds no matches, the page is an image and needs OCR.
Does OCR upload my document?
With PDFNest, no — recognition runs entirely in your browser, so your document never leaves your device.