OCR Explained: Turning Scanned PDFs into Editable Text

Understand Optical Character Recognition (OCR), how it reads scanned documents, and when to use it.

OCR stands for Optical Character Recognition. It is the technology that turns a picture of text — like a scanned page or a photo of a receipt — into real, selectable, searchable characters.

Why scanned PDFs need OCR

When you scan a document, the result is an image. Your computer sees pixels, not letters, so you cannot search, select or copy the text. OCR analyses the shapes in the image and matches them to characters, adding an invisible text layer to the PDF.

How OCR works, step by step

• Pre-processing cleans up the image: straightening, removing noise and boosting contrast
• Segmentation finds lines, words and individual characters
• Recognition matches each shape to a character using trained models
• Post-processing uses dictionaries to fix likely errors

Getting the best OCR results

Scan at 300 DPI or higher, keep pages straight, and use good lighting for photos. The cleaner the source image, the more accurate the recognised text will be.