What is OCR? How Text Recognition Works in PDFs
What it is
OCR (Optical Character Recognition) is technology that converts images of text—such as scanned documents, photos of pages, or PDF images—into machine-readable and editable text. Modern OCR achieves 95-99% accuracy on clear documents.
Why it matters
Scanned PDFs are essentially images—you cannot search, copy, or edit the text. OCR makes documents accessible, searchable, and editable. It also enables screen readers to read content for visually impaired users.
How it works
OCR works in stages: (1) Image preprocessing cleans and straightens the image, (2) Character segmentation identifies individual letters, (3) Pattern recognition matches characters against known fonts, (4) Language processing corrects errors using dictionaries. AI-powered OCR adds context understanding for higher accuracy.
Cost
Free for basic OCR with iReadPDF (3 uses per day on free tier). Premium plans include unlimited OCR and AI-enhanced recognition.
Time
Typically 10-60 seconds per page depending on complexity. A 10-page scanned document processes in approximately 2-5 minutes.
Risk
Low to medium. OCR is highly accurate (95-99%) for printed text. Handwriting recognition is less reliable (70-90%). Always proofread OCR results for important documents.
Who it's for
- Anyone with scanned paper documents
- Offices digitizing paper archives
- Researchers working with historical documents
- Legal professionals processing scanned contracts
- Students needing searchable study materials
- Accessibility compliance officers
Limitations
- Handwritten text has lower accuracy than printed text
- Poor image quality (blurry, low resolution) reduces accuracy
- Complex layouts with tables or columns may need manual correction
- Non-Latin scripts may have varying accuracy levels
- Decorative or unusual fonts may not be recognized
Common mistakes to avoid
Running OCR on already-text PDFs
Consequence: Creates duplicate text layer, may cause display issues
Instead: Check if PDF already contains selectable text before running OCR
Using low-resolution scans
Consequence: Poor OCR accuracy, missing characters
Instead: Scan at 300 DPI minimum; 600 DPI for small text
Not proofreading OCR results
Consequence: Errors in critical documents like contracts or legal filings
Instead: Always review OCR output for important documents
Special cases and exceptions
Mixed handwriting and printed text
AI-OCR can distinguish between handwritten and printed text, processing each appropriately. Handwritten sections may require manual review.
Applies to: Forms with handwritten entries, annotated documents
Multi-language documents
Modern OCR supports 100+ languages and can detect language automatically. Accuracy varies by script complexity.
Applies to: Translated documents, international contracts
Historical documents with old fonts
Specialized OCR models exist for historical typefaces. Standard OCR may struggle with Gothic or blackletter fonts.
Applies to: Archival research, genealogy documents
Frequently Asked Questions about OCR (Optical Character Recognition)
How accurate is OCR?
Modern OCR achieves 95-99% accuracy on clear, printed documents at 300+ DPI. Handwriting recognition is typically 70-90% accurate depending on legibility.
Can OCR read handwriting?
AI-powered OCR can read clear handwriting with 70-90% accuracy. Cursive and messy handwriting has lower accuracy and may require manual correction.
Does OCR work on all languages?
Yes. iReadPDF OCR supports 100+ languages including Chinese, Japanese, Arabic, and Cyrillic scripts. Accuracy varies by language complexity.
Related iReadPDF Tools
How we verify this information
- Research official PDF specifications and industry standards
- Test features using iReadPDF tools with real documents
- Verify accuracy with PDF industry experts
- Update content when specifications or best practices change
Data sources
- Adobe PDF Reference
- ISO 32000-2
- iReadPDF internal testing
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