What is OCR and how does it work?
OCR stands for Optical Character Recognition. It is the technology that converts an image of text — a photograph, a scan, a screenshot — into actual machine-readable text characters that a computer can index, search, and copy.
When you scan a document, the scanner captures it as a photograph. The PDF contains that photo — not text. OCR analyzes the shapes of letters in the image, matches them against character patterns it has learned during training, and outputs the corresponding text. The result is a new PDF with an invisible text layer laid over the original image — the document looks identical, but you can now search it with Ctrl+F and copy text from it.
Scanned PDF vs digital PDF — know the difference
Scanned PDF (image)
Created by a scanner or camera. Contains a photo of the page. Text cannot be selected or searched. Needs OCR to become searchable. File size is usually large.
Digital PDF (text)
Created from Word, InDesign, or printed to PDF. Contains actual text characters. Text is selectable and searchable. Does not need OCR — convert directly with PDF to Word.
To test which type you have: open the PDF and try to select text with your cursor. If you can highlight individual words, it is a digital PDF. If the cursor only draws a selection box over an image, it is a scanned PDF that needs OCR.
Step-by-step: how to OCR a PDF
Open the OCR PDF tool
Go to hugmypdf.com/tools/ocr-pdf. OCR requires server processing — your file is uploaded securely and deleted immediately after.
Upload your scanned PDF
Drag and drop the file. Files up to 50MB are supported. Multi-page documents are processed all at once.
Select the document language
For best accuracy, select the primary language of the document. English is the default. The tool supports 100+ languages.
Download the searchable PDF
OCR takes 10–60 seconds depending on page count. The output PDF looks identical but is now fully searchable and copy-pasteable.
Real-world use cases
OCR accuracy — what to expect
Tesseract (the OCR engine used by HugMyPDF) achieves 97–99% character accuracy on clean, high-resolution scans. In practice, this means one or two characters wrong per hundred — usually in punctuation, numbers, or unusual character shapes.
Accuracy drops with: low resolution (under 200 DPI), heavy background patterns or watermarks, skewed or curved pages, handwriting (OCR is not designed for handwriting), and very small fonts.
Best practice: Scan at 300 DPI or higher. Scan in grayscale or black-and-white rather than color (reduces file size and improves contrast). Ensure pages are flat with no curl at edges. Good scan quality makes a significant difference in OCR output quality.