What is 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 produce a text layer or separate text output. Accuracy varies by engine, language, typography, scan quality, and layout.
OCR quality drops on poor scans (skew, low resolution, faded ink), dense formulas, multi-column layouts, and scripts with limited training data. For important documents, use a clear scan, run OCR with a suitable engine, and review the output before relying on quotations or citations.
Summio currently requires a text layer and does not run OCR on image-only scans. Apply OCR before uploading, keep the PDF within 50 MB and 1,000 pages, and review the Privacy Policy for data handling and provider terms.
Read more about SummioCommon questions
Is PDF OCR free?
Apple’s built-in tools, Adobe products, and other PDF utilities offer different OCR capabilities. Summio currently requires a text layer, so run OCR on an image-only scan before uploading it within the file and page limits.
How accurate is PDF OCR on scanned books?
Clear, high-resolution printed pages generally produce better OCR results. Skew, faded copies, handwriting, unusual fonts, and complex layouts can require manual review.
Does OCR work on handwritten PDFs?
Handwriting recognition varies widely by engine, script, image quality, and writing style. Treat the result as a draft and review it manually before relying on quotations or important details.