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How to OCR PDF: Extract Text from Scanned Documents

By PDFGo Team
PDFOCRText ExtractionScannedGuide

How to OCR PDF: Extract Text from Scanned Documents

OCR (Optical Character Recognition) converts scanned PDFs and images into searchable, editable text. This is essential for working with scanned documents, old papers, and image-based PDFs.

Why Use OCR on PDFs?

There are many important reasons to use OCR:

  • Make documents searchable: Find text in scanned documents
  • Extract text: Get text from scanned pages for editing
  • Edit scanned content: Modify text from scanned documents
  • Accessibility: Make scanned documents accessible to screen readers
  • Digital archives: Convert paper documents to searchable digital files
  • Text extraction: Pull text from images and scanned pages

What is OCR?

OCR (Optical Character Recognition) is technology that:

  • Recognizes text: Identifies text in images and scanned documents
  • Converts to text: Transforms image text into editable text
  • Preserves layout: Maintains document structure and formatting
  • Multi-language: Supports multiple languages

How OCR Works

Step 1: Select Your PDF

Choose the scanned PDF or image-based PDF you want to process with OCR.

Step 2: Configure OCR Settings

Set your OCR preferences:

Languages:

  • English: Most common
  • Multiple languages: Select all languages in your document
  • Language-specific: Choose specific languages for better accuracy

OCR Type:

  • Skip Text: Only OCR pages without existing text
  • Force OCR: OCR all pages regardless of existing text
  • Normal: Standard OCR processing

Render Type:

  • HOCR: HTML-based OCR output
  • Sandwich: Text layer over original image

Step 3: Process with OCR

Run OCR processing. The tool will:

  • Analyze each page
  • Recognize text characters
  • Extract text content
  • Create searchable text layer

Step 4: Review Results

Check the OCR'd PDF:

  • Verify text accuracy
  • Check for recognition errors
  • Ensure all text was extracted
  • Test search functionality

Step 5: Download

Download your searchable PDF with extracted text.

OCR Accuracy Factors

Image Quality

  • High resolution: Better quality scans produce better OCR results
  • Clear text: Sharp, clear text is recognized more accurately
  • Contrast: Good contrast between text and background
  • Straight pages: Properly aligned pages improve accuracy

Document Type

  • Printed text: Most accurate OCR results
  • Handwriting: Less accurate, may need manual review
  • Mixed content: Text and images may need different processing
  • Old documents: May have lower accuracy due to quality

Language Support

  • Single language: More accurate for one language
  • Multiple languages: Select all languages present
  • Special characters: Some languages may need specific settings

Common Use Cases

Scanned Documents

Convert scanned paper documents into searchable, editable PDFs.

Old Archives

Digitize old documents, books, and archives with OCR.

Forms and Applications

Extract text from scanned forms and applications for digital processing.

Receipts and Invoices

Extract data from scanned receipts and invoices for record keeping.

Legal Documents

Convert scanned legal documents into searchable PDFs for legal research.

Tips for Best OCR Results

Before OCR

  1. Improve scan quality: Use high-resolution scans (300 DPI or higher)
  2. Clean images: Remove smudges, marks, and artifacts
  3. Straighten pages: Ensure pages are properly aligned
  4. Good contrast: Ensure text is clearly visible

During OCR

  1. Select languages: Choose all languages in your document
  2. Choose OCR type: Use "Force OCR" for scanned documents
  3. Be patient: OCR processing can take time for large documents
  4. Test settings: Try different settings for best results

After OCR

  1. Review accuracy: Check extracted text for errors
  2. Correct errors: Manually fix recognition mistakes
  3. Test search: Verify text is searchable
  4. Verify completeness: Ensure all text was extracted

Best Practices

  1. High-quality scans: Start with the best possible scan quality
  2. Language selection: Accurately identify document languages
  3. Review results: Always review OCR output for accuracy
  4. Manual correction: Be prepared to correct recognition errors
  5. Test search: Verify that text is searchable after OCR

Understanding OCR Limitations

Accuracy Expectations

  • Printed text: 95-99% accuracy for clear printed text
  • Handwriting: Lower accuracy, often needs manual review
  • Poor quality: Low-quality scans have lower accuracy
  • Complex layouts: Complex formatting may affect accuracy

Common Errors

  • Similar characters: O/0, I/l/1 confusion
  • Font recognition: Unusual fonts may be misrecognized
  • Formatting: Complex formatting may not be preserved
  • Special characters: Some special characters may not be recognized

Troubleshooting

Low Accuracy

If OCR accuracy is low:

  • Improve source image quality
  • Use higher resolution scans
  • Ensure good contrast
  • Check language settings

Missing Text

If text is missing:

  • Verify image quality
  • Check if text is actually in the image
  • Try different OCR settings
  • Review for recognition errors

Search Not Working

If text isn't searchable:

  • Verify OCR was completed
  • Check that text layer was created
  • Ensure PDF supports text search
  • Try re-processing with OCR

Conclusion

OCR is essential for working with scanned documents and making them searchable and editable. While accuracy varies by document quality, modern OCR tools provide excellent results for most documents.

Need to extract text from a scanned PDF? PDFGo's OCR tool supports multiple languages and OCR types, converting scanned documents into searchable, editable PDFs. Process your scanned documents with cloud-powered OCR. Try PDFGo today!