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PDF OCR quality checker

Classify each PDF page as born digital, OCR layer, or image only, score the text with dictionary, garbage symbol, and letter digit checks, and list pages to re-OCR.

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This tool audits text that already exists in the file; it never performs OCR. Each page is classified by what pdf.js extracts: a page with no letter words is a scan or a blank, and a page whose glyphs are drawn invisible (text render mode 3) carries a hidden OCR layer. Pages rate poor at more than 5 percent letter/digit mix like vi11age or c1erk, more than 5 percent garbage symbols such as replacement and private-use characters, or a dictionary share under 70 percent when at least 20 words are checkable; between those marks and 1 percent, or a share under 85 percent, they rate fair. The dictionary holds 25,322 common English words with plural trimming, and capitalized unknown words count as names rather than damage, so a short English page under 20 words gets no verdict. Two faults stay invisible to every check: real word substitutions such as form for from, and born-digital pages whose fonts ship no Unicode map, which is a font problem rather than an OCR one. Everything runs in your tab and nothing is uploaded.
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