OCR Hangs on Large PDFs with EnglishFast Secondary Language
IronOCR can stall mid-processing on large PDFs when OcrLanguage.EnglishFast is added as a secondary language. No exception is thrown and execution never resumes, so the request appears to run forever.
Execution stops at the ocr.Read() call. No exception is thrown and no error is logged.The stall is triggered by the EnglishFast model when it sits in the secondary language list on Windows. It has been reproduced in our testing across IronOCR 2025.12.3, 2026.1.2, 2026.2.1, and 2026.3.3 through 2026.7.2. Until a fixed version is published, treat any release in that range as potentially affected. Reordering EnglishFast relative to the other secondary languages does not help.
Solution
1. Find the secondary language configuration
Locate any call to AddSecondaryLanguage that passes OcrLanguage.EnglishFast in your OCR setup.
// This line causes the hang on large PDFs
ocr.AddSecondaryLanguage(OcrLanguage.EnglishFast);2. Remove EnglishFast and keep English primary
Delete or comment out the offending call. Set OcrLanguage.English as the primary language so English recognition quality is preserved, and leave your other secondary languages in place, they are unaffected.
// ocr.AddSecondaryLanguage(OcrLanguage.EnglishFast);
var ocr = new IronTesseract
{
Language = OcrLanguage.English
};
ocr.AddSecondaryLanguage(OcrLanguage.Hindi);
ocr.AddSecondaryLanguage(OcrLanguage.Marathi);Dropping EnglishFast removes the fast English model, but keeping OcrLanguage.English as the primary language maintains coverage for documents with significant English text.
3. Re-run the affected PDF
Process the document again. It should now complete through all pages without stalling.
Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.
