How to Translate a Research Paper PDF in 2026: DeepL, Google Translate, ChatGPT, Readable and On-Device Translation Compared

There are five realistic ways to translate a research paper PDF today: a document translator such as DeepL, Google Translate's free document mode, a chat assistant such as ChatGPT, a service built for papers such as Readable, or a reader that translates on your own device. They differ less in translation quality than in three things: how many papers you can translate per month and how big a file may be, what a year of it costs, and whether your paper is uploaded to someone's server. This article compares them on those three things, with the limits and prices as published on 28 October 2026, and ends with what on-device translation, which is what we build, cannot do yet.

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The five options, side by side

The rows are not alike, and that is the point. The first three give you a translated file or text and leave the reading to you. The last two are built around papers: Readable returns a PDF that looks like the original, and Rectoly translates inside the reader, where you can keep the original beside the translation and your highlights land on the original text.

What each one is good at

DeepL is the translator most researchers already use for a paragraph at a time, and its document mode keeps the original format well. The constraint is the quota: the free version allows one file a month and the Individual plan three, so it suits translating the occasional paper in full, not a reading list. Above that you are on a Team plan priced per user.

Google Translate is free and takes a whole PDF up to 10 MB and 300 pages. The result is a translated document rather than a readable paper: a two-column journal layout does not survive reliably, and figures and equations come back as they can. For a quick look at a paper in a language you do not read at all, it is hard to beat; for reading twenty papers for a thesis, it is a lot of reassembly.

ChatGPT and the other chat assistants translate prose well and let you ask about the paragraph afterwards, which none of the others do. A paper is uploaded or pasted in pieces, the translation comes back as text, and you keep track of where you are. Numbers and citations can be altered in the retelling, so they need checking against the original. Plus is $20 a month in the US, and the free tier is enough for a few paragraphs.

Readable is a Japanese service built for exactly this: upload an English paper, get a Japanese PDF with the layout intact, with no cap on the number of files. Its cheaper plan is English into Japanese only; the Premium plan adds 200 source languages, larger files and a term dictionary. If you read papers in Japanese and want a translated PDF to print or annotate elsewhere, it is the closest thing to a specialist.

On-device translation in Rectoly is a different shape. The translation model is downloaded once, about 2.5 GB, and runs on the iPad, phone or computer itself; after that it works with the network off and nothing is uploaded. In Reading Mode each paragraph's translation sits under the original, so you read in your language and check against the source without leaving the page; on the PDF page you can switch the text to the translation with columns, headings and figures where they were, and back. Mathematics, numbers, citation markers and the paper's own terms are masked before translation and checked afterwards, and a paragraph that fails the check is shown in the original rather than as a wrong guess. The engine translates ahead of you in the paper you have open. It is part of Rectoly for Zotero, Rectoly for Mendeley and the student app Rectoly: How to Read Papers, and there is no per-page fee and no API key.

What a year of translating papers costs

The prices above, over one year and three years, for one person. The quota column matters as much as the price: a graduate student reads far more than three papers a month.

Prices in each service's own currency, annual billing where that is the published price, taxes as each site states them. Rectoly's prices are the App Store and rectoly.com prices in US dollars; the App Store shows them in your local currency. Over three years, the cheapest plan that translates an unlimited number of papers costs ¥28,800 at Readable or €899.64 at DeepL at the Team tier, against $19.99 once for the Zotero edition of Rectoly, which also includes the reader. That is the cost argument, and it is a real one. The next two sections are the other half of the comparison.

Where your paper goes

Every service in the table except the last one works by uploading the PDF to the service's servers, translating it there, and sending the result back. For a published paper that is only a question of the service's terms. For a manuscript you are reviewing, a draft nobody has seen, a thesis chapter from a student, or data under an agreement, it is a question you have to answer before you upload, and the answer is often no. On-device translation exists for that case: the model runs on the hardware in front of you, and an iPad too small to run it can hand the paragraphs to Rectoly on your own computer over your own network, encrypted for that pair of machines, and never through our servers.

What on-device translation cannot do yet

Being honest about the limits is part of the comparison.

• English source only. Rectoly translates English papers into 20 languages (Japanese, Chinese, Korean, German, Spanish, French, Italian, Portuguese, Dutch, Danish, Swedish, Norwegian, Polish, Turkish, Indonesian, Vietnamese, Russian, Ukrainian, Arabic, and on Apple devices Hindi and Thai through the system translator). A paper written in German or Chinese is not translated. DeepL, Google and Readable's Premium plan translate between many more pairs.
• A small model. It runs on a tablet, so it is far smaller than the models behind the cloud services. We measure each language on a set of real papers before offering it, and we would rather show you the original than a wrong guess, which is what the checks do. We do not claim the prose is better than DeepL's.
• Hardware. Translating on the device needs about 8 GB of memory and 3 GB of free space; on Windows and Linux a Vulkan-capable graphics card makes it quick, and without one only the paragraphs on screen are translated. A smaller tablet or phone works by pairing with your computer.
• No translated file to hand on. The translation is for reading inside Rectoly. You can copy a translated passage, and translations are stored with the paper so your other devices show them, but there is no "export translated PDF" as Readable produces.
• Mathematics on the PDF page. On Windows, Linux and Android, a paragraph with equations is left in the original on the PDF page; its translation is in Reading Mode. References and tables stay as printed everywhere.

How to translate a paper well, whichever tool you use

• Translate a paragraph at a time, with the original in view. Reading only a translation teaches you none of the field's terms, and the terms are what you will need in your own writing.
• Keep the technical terms in the source language, or build a short glossary: the same term translated two ways in one paper is the most common confusion. Rectoly builds a glossary from the paper's title and opening before it starts; Readable's Premium plan and DeepL's paid plans have dictionaries.
• Check every number, unit and citation marker against the original. Translation systems are weakest exactly there, and it is where a misreading costs most.
• Decide what may be uploaded before you start, and use an offline or on-device tool for anything that may not.

Frequently asked questions

Can DeepL translate a PDF research paper?

Yes. DeepL's document translation takes a PDF and returns a translated copy in the same format. The free version allows one file a month up to 5 MB; the Individual plan three files a month up to 30 MB; the Team and Business plans 20 and 100 files per user per month. The file is uploaded to DeepL's servers for translation.

Is there a free way to translate a research paper PDF?

Google Translate's document mode is free for files up to 10 MB and PDFs up to 300 pages, and DeepL's free version translates one file a month. Both return a translated document rather than a readable paper, and both upload the file. Rectoly's on-device translation is free during the 14-day trial and then part of the one-time purchase.

Can ChatGPT translate a research paper?

It translates prose well, in pieces, and you can ask it about the paragraph afterwards. The limits are practical: a paper goes in by upload or in sections, the translation comes back as text, and numbers and citations should be checked against the original. ChatGPT Plus is $20 a month in the US.

Can I translate a paper offline, without uploading it?

Yes, with a translator that runs on the device. In Rectoly the 2.5 GB model is downloaded once and translation then works with the network off; the paper never leaves the device, or your own computer if the tablet hands the work to it. See translation on the iPad and translation on Windows, Mac and Linux.

Does the translation keep the layout of the PDF?

Readable returns a new PDF with the layout intact. Rectoly keeps the layout by switching the text on the PDF page in place, columns and figures where they were, and by putting each paragraph's translation under the original in Reading Mode. DeepL keeps the document format; Google Translate's PDF output does not reliably preserve a two-column layout. ChatGPT returns text.

Does Rectoly translate papers written in Japanese, German or Chinese into English?

Not yet. Rectoly translates English papers into 20 languages; the source language has to be English. For the other direction, use DeepL, Google Translate or Readable's Premium plan.

How much does translating papers cost per year?

DeepL Individual is €89.88 a year for three files a month; Readable Pro Standard is ¥9,600 a year for unlimited English-to-Japanese files; ChatGPT Plus is $240 a year; Google Translate is free with a 10 MB limit per file. Rectoly's translation is included in a one-time purchase of $19.99 (Zotero edition), $49.99 (Mendeley edition) or $9.99 (the student app), with no yearly cost after that.

Is it legal to translate a research paper?

Translating a paper for your own reading is ordinary private use. Publishing or distributing a translation is a derivative work that needs the rights holder's permission, as it would in any language. Uploading a paper to a service is governed by the paper's licence and the service's terms; a manuscript under review or embargo usually may not be uploaded anywhere. This is not legal advice; when in doubt, ask your library.