How OCR Works on Scanned PDFs
Learn what OCR adds, why recognition fails, and how to evaluate searchable output.
Images become candidate characters
A scanned PDF often contains page images rather than text. OCR analyzes shapes, groups them into lines and words, and places a hidden or visible text layer over the image. The original pixels and recognized text are separate representations.
Input quality controls accuracy
Skew, blur, shadows, low contrast, unusual fonts, handwriting, tables, and mixed languages reduce accuracy. Selecting the correct language model helps the engine distinguish similar characters.
- Scan near 300 dpi for ordinary printed text
- Deskew and crop dark borders
- Select only the languages present in the document
Always verify important text
OCR confidence is not legal or factual certainty. Search for names and numbers, copy representative passages, and compare them with the page image. Human review is essential for contracts, financial records, medical documents, and accessibility remediation.