OCR PDF
识别扫描文档中的文本，以便复制和搜索。
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Free PDF OCR Online — Make Scanned PDFs Searchable and Copyable
Convert scanned PDFs and image-based PDFs into fully searchable, copyable text documents. Powered by Tesseract OCR — supports 40+ languages including English, French, Spanish, Arabic, Chinese and Japanese.
What OCR does to your PDF
A scanned PDF is essentially a photograph — text is drawn as pixels, not encoded as machine-readable characters. Without OCR, you cannot search for a word, copy a sentence, index the document in Google, or have it read by a screen reader. After OCR, an invisible text layer is added beneath the visual content: the document looks identical but text is now selectable, copyable and searchable. This is called a "searchable PDF" or "PDF/A with text layer."
Accuracy and scan quality tips
OCR accuracy depends directly on scan quality. For best results: scan at 300 DPI minimum (600 DPI for small text or receipts); ensure pages are flat, not curved; avoid shadows across text; use good contrast (black text on white background). At 300 DPI with clean scans, Tesseract achieves 95%+ accuracy for standard Latin-script languages. Handwritten text, decorative fonts and very small text (below 8pt) have lower accuracy.
Visual appearance after OCR
The visual appearance of your PDF remains identical to the original scan. The text layer is added invisibly beneath the image layer — users see the scanned page, but software can now read and index the text. File size increases slightly due to the added text data.
FAQ
Does OCR change the visual appearance of my PDF?
No. The visual scan is preserved identically. Only an invisible text layer is added underneath the image layer.
Which languages does the OCR support?
40+ languages including English, French, Spanish, German, Italian, Portuguese, Arabic, Chinese (simplified & traditional), Japanese, Korean, Russian and more.
My scanned PDF is in color — does OCR still work?
Yes. OCR works on color, grayscale and black & white scans. Color scans may produce slightly larger output files.
What DPI should my scan be for best results?
300 DPI minimum for body text. 600 DPI for small text, receipts or footnotes. Below 150 DPI, accuracy drops significantly.
Can OCR process a multi-page scanned PDF?
Yes. All pages are processed in a single operation. OCR is applied to every page, regardless of page count.
Will OCR work on PDFs that are already text-based (not scanned)?
OCR is designed for image-based or scanned PDFs. If your PDF already contains embedded text (created from Word, InDesign etc.), it is already searchable — no OCR needed.
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