PDF Translator (English ↔ Korean)

Upload a text-based PDF and get a paragraph-by-paragraph English→Korean or Korean→English translation. Review original and translated text side by side (and edit it), then download as plain text, HTML, or a PDF that keeps the original paragraph positions. Nothing is uploaded to a server.

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How to use it

Drop in the PDF you want translated, or click to choose it. Only text-based PDFs are supported; scanned image PDFs need OCR first (see below).
Pick a translation direction (English→Korean / Korean→English) or leave it on auto-detect. For long documents you can choose a page range (default: the first 5 pages).
Click "Start translating". The first run downloads the translation AI model (about 630MB) once, then translates paragraph by paragraph, showing progress and an ETA. You can pause or cancel at any time.
Once done, review the original and translation side by side and edit the translation directly. When you're happy with it, download as plain text (.txt), HTML, or a PDF that keeps the original layout.

How paragraphs are detected

Dagochim's PDF Translator reads every text fragment inside the PDF (its position, font size, and line spacing) and automatically groups lines that look like the same paragraph. Lines with a noticeably larger font size are treated as headings and shown in bold; lone numbers sitting alone near the top or bottom of a page (likely page numbers) are excluded from translation. This grouping isn't perfect though - documents with tables or multiple columns may have paragraphs grouped slightly differently or out of the expected order.

How the format-preserving PDF is built

When you download the "format-preserving PDF", the original PDF pages are kept as-is: the tool draws a white rectangle over each original paragraph's area, then draws the translated text back into that same spot. If the translation is longer than the original, the font size automatically shrinks to try to fit the same box. To display both Korean and Latin characters, the tool embeds (and subsets) the Nanum Gothic font inside the PDF, which can slightly increase file size. Tables, multi-column layouts, and text overlaid on images may end up slightly misaligned - please keep that in mind for complex documents.

About the translation AI model

This tool runs M2M100, an open-source multilingual translation model released by Meta AI, directly in your browser. The model file is fairly large (about 630MB), so it isn't downloaded automatically - it only downloads once you click "Start translating". We recommend using Wi-Fi for that first download; after that, the model is cached in your browser and future translations start instantly. Paragraphs you've already translated are also cached, so re-running a translation on the same text is instant.

Open-source credits

M2M100 (facebook/m2m100_418M) (Meta AI, MIT License) — a multilingual translation model covering 100 languages, including English and Korean.
Transformers.js (Hugging Face, Apache License 2.0) — the library that loads and runs the AI model in the browser.
ONNX Runtime Web (Microsoft, MIT License) — the inference engine that runs the model via WASM.
PDF.js (Mozilla, Apache License 2.0) — reads text position and font size out of the PDF.
pdf-lib (Andrew Dillon and contributors, MIT License) — builds the new PDF with the translated text.
fontkit (@pdf-lib/fontkit) (MIT License) — lets pdf-lib embed and subset a Korean font inside the PDF.
Nanum Gothic (NAVER, SIL Open Font License 1.1) — the font embedded in the "format-preserving PDF" output, covering both Korean and Latin text.

Frequently asked questions

Can it translate scanned PDFs (images)?

This tool only translates text-based PDFs directly. For a PDF made from scanned pages or photos, first extract the text with Dagochim's Image-to-Text (OCR) tool, then copy that text and translate it.

How good is the translation quality? Is it as accurate as a professional translator?

This produces a machine-translation draft using the open-source M2M100 model. It handles everyday sentences reasonably well, but technical terminology, complex sentences, and formal documents like contracts can come out wrong or awkward. Always have a human review important documents after translation.

Is my file sent to a server?

No. Reading the PDF, extracting text, AI translation, and generating the new PDF all happen locally in your browser. The first time you click translate, the tool downloads the translation AI model (about 630MB) once - that download is just the model itself; the PDF or text you work with is never uploaded anywhere.

Does the format-preserving PDF look exactly like the original?

It stays close but isn't pixel-perfect. The tool covers each original paragraph's area with a white box and draws the translated text back into that same spot, so simple single-column documents usually look clean, but tables, multi-column layouts, or text overlaid on images may shift slightly or auto-shrink in font size.