OCR PDF

Accuracy depends heavily on your document's quality, but our Tesseract.js OCR engine typically achieves 95-99% accuracy with clear, high-contrast documents. Factors that improve accuracy include: 300+ DPI resolution, black text on white background, standard fonts (Arial, Times, Helvetica), and good lighting for photographed documents. Accuracy decreases with: handwritten text (60-80%), complex backgrounds behind text, very low resolution scans, skewed or rotated pages, and unusual fonts. For best results, use high-quality scans (300 DPI or higher), ensure text is straight and clear, and crop out unnecessary borders. The OCR engine automatically handles most common document types including printed text, typewritten pages, and clear computer-generated documents.

No, absolutely not! The original images are preserved exactly as they were. Our OCR process creates an invisible text layer that sits on top of the original image—like a transparent sheet with text printed on it. Your PDF looks visually identical to the original, but now has selectable, searchable text embedded in it. This approach is called 'image-over-text' layering. The visual quality of your document remains unchanged—you won't see any difference when viewing or printing. Only when you try to select text (highlight with your mouse) or use the search function will you notice the new capability. This preservation of original images is especially important for archival purposes where maintaining the authentic appearance of historical documents matters.

Processing time varies by document complexity and your device's speed, but typically takes 5-10 seconds per page for standard text documents. A 10-page document usually completes in 1-2 minutes. Factors affecting speed include: page resolution (higher DPI = slower), text density (more text = slower), image complexity, and your computer's processing power. The Tesseract.js engine runs in a Web Worker to keep your browser responsive during processing. For very large documents (100+ pages), consider processing in batches. Unlike cloud OCR services where processing time includes upload and download delays, our local processing means the time you see is purely recognition time—no network latency.

No, absolutely not. All OCR processing happens locally in your browser using WebAssembly technology. Your documents never leave your device, never touch our servers, and are never accessible to us or any third party. Tesseract.js—the OCR engine we use—is loaded directly into your browser and runs entirely on your computer. This is fundamentally different from cloud OCR services like Google Vision, AWS Textract, or Azure Computer Vision, which require uploading your documents to their servers for processing. With PDF Zone, you can process sensitive financial records, medical files, legal contracts, and personal documents with complete privacy assurance. Even if you disconnect from the internet after loading the page, the OCR will continue to work.

The OCR tool recognizes over 100 languages and scripts including: English, Spanish, French, German, Italian, Portuguese, Dutch, Russian, Chinese, Japanese, Korean, Arabic, Hebrew, Hindi, and many more. Tesseract.js includes trained language models for Latin-based scripts, Cyrillic, CJK (Chinese/Japanese/Korean), Arabic, and others. The text recognition happens automatically without manual language selection—the engine attempts to detect and recognize all supported languages simultaneously. For documents with mixed languages, the OCR will recognize each section appropriately. The accuracy is highest for Latin-based languages (English, Spanish, French, etc.) as these have the most training data, but all supported languages achieve professional-quality recognition with clear documents.

Currently, we support PDF files as input. If you have image files (JPG, PNG, TIFF, BMP) that need OCR, first convert them to PDF using our 'Images to PDF' tool, then run OCR on the resulting PDF. The output is always a PDF with the invisible text layer added. For best results, ensure your input PDF contains clear, legible text. Very low-quality scans or extremely blurry images may not produce accurate OCR results. We recommend 300 DPI resolution minimum for good accuracy. The tool works with multi-page PDFs and will process all pages sequentially.

Handwriting recognition is supported but with lower accuracy than printed text (typically 60-80% vs 95%+ for print). The accuracy depends on how neat and legible the handwriting is. Printed or typed documents work best. For handwritten forms or documents, you may need to manually correct some recognized text. Tesseract.js has some capability for recognizing cursive and block handwriting, but it's not as reliable as printed text recognition. If you have critical handwritten documents, we recommend reviewing and correcting the output carefully. For printed documents, the accuracy is excellent and requires minimal or no correction.