PDF OCR
PDF OCR (Optical Character Recognition) is the process of converting the image-based text inside a scanned PDF into selectable, searchable, machine-readable text.
There are two kinds of PDF: text-layer PDFs (born-digital, e.g. exported from Word or LaTeX) where the text is directly readable, and scanned PDFs (photographed or scanned paper) where the page is just a picture of text. Software cannot search, copy, or summarise the second kind without OCR.
OCR engines analyse the page image, detect lines and characters, recognise glyphs, reconstruct words and paragraphs, and finally produce a text layer added back to the PDF (or a separate text file). Modern OCR uses deep neural networks instead of older template-matching algorithms — accuracy on clean printed text is now above 99% for major languages.
OCR quality drops on poor scans (skew, low resolution, faded ink), dense formulas, multi-column layouts, and scripts with limited training data. Best practice for important documents is to scan at 300 DPI in colour, run OCR with a modern engine, and review the output before using it for citations.
When you upload a PDF to Summio, the app detects whether OCR is needed and runs it automatically before summarising. The original PDF and the OCR text both stay inside your account — they are not used to train AI models.
Read more about Summio →Common questions
Is PDF OCR free?
Apple’s built-in PDFKit, Adobe Acrobat Reader, and most modern PDF tools include OCR for free or at low cost. Summio bundles OCR into PDF summarisation — no separate step.
How accurate is PDF OCR on scanned books?
For well-scanned printed pages in major languages, modern OCR is 99%+ accurate at the character level. Drop scans, faded photocopies, and unusual fonts can fall below 90% — manual cleanup is needed.
Does OCR work on handwritten PDFs?
Older OCR engines do not handle handwriting well. Newer ML-based OCR (Apple’s Vision framework, Google’s Document AI) handle clear printing reasonably and cursive script poorly.