# Summarizing PDFs, documents, and long threads with AI

> How ChatGPT, Claude, Gemini, Copilot, and Gemini Notebook summarize PDFs and long documents as of November 2026, their file limits, and how to check a summary.

To **summarize documents** with AI, you can attach a file to a chat in ChatGPT, Claude, Gemini, or Copilot, use a tool that answers only from your sources, such as Gemini Notebook (formerly NotebookLM) or Copilot Notebooks, or use the summaries built into Gmail and Outlook. Each has its own file limits, and Microsoft says Copilot may read only the beginning of a very long document.

**Key takeaways**

1. Google says that even when sources are shown, Gemini in Workspace can leave some out, cite a document it did not use, or make up a source.
2. Gemini Notebook answers only from the sources in a notebook, with up to 500,000 words or 200 MB per source and 50 sources per notebook without a paid plan.
3. Gmail's AI Overview summary of an email thread is available to all Gmail users worldwide in supported languages, as of November 10, 2026.


## Summarizing documents with AI

A summary is only useful if you can trust what it left out as much as what it kept. This page is part of [using AI for everyday tasks](/guides/ai-at-work/everyday-tasks/) and covers how the main assistants summarize PDFs, reports, and long email threads, with the limits their help pages published as of November 10, 2026; Microsoft's note on [how document length affects Copilot](https://support.microsoft.com/en-us/microsoft-365-copilot/how-reference-and-document-lengths-affect-copilot-responses) is the one to read first.

For a single report, attaching the file to a chat is enough. For a set of documents you will question again, a notebook that answers only from your sources is safer. For email, the summary built into your mailbox saves the copy and paste. In all three cases, check at least one citation for each point you plan to use.

### Three ways to get a summary

| Approach | Examples | Best for | Watch out for |
|---|---|---|---|
| Attach a file to a chat | ChatGPT, Claude, Gemini, Copilot | A single PDF, contract, or report | Plan limits; parts of a long file may be skipped |
| A notebook limited to your sources | Gemini Notebook, Copilot Notebooks | Several documents you will come back to | Source limits and usage quotas |
| The summary in your mailbox | AI Overview in Gmail, Summary by Copilot in Outlook | Long email threads | Covers the thread, not the whole inbox |

Gemini Notebook only answers from the notebook's sources and cites exact passages: hover over a citation to read it, click to open it in context. Copilot Notebooks likewise uses only the references you add.

### File limits as of November 10, 2026

| Tool | Limits published by the company |
|---|---|
| ChatGPT | 512 MB per file; documents capped at 2 million tokens; three uploads a day on Free |
| Claude | 500 MB per file and 20 files per chat; PDFs up to 1,000 pages; images and charts are read up to 100 pages |
| Gemini app | 10 files per message, 100 MB each; a context window of 32,000 tokens without a plan and up to 1 million on Pro and Ultra |
| Gemini Notebook | 500,000 words or 200 MB per source; 50 sources per notebook without a plan, 100 on Plus, 300 on Pro |
| Copilot Notebooks | 50 sources with Copilot Chat, 300 with a Copilot license |
| Copilot in Word | A word limit per prompt, not published |

The companies do not measure these limits the same way, in tokens, pages, words, or files, so the table does not rank the tools. A token is a piece of a word; Anthropic puts 200,000 tokens at about 500 pages of text.

### Long documents: split them

Microsoft says that, for a summary, Copilot may focus only on the beginning of a long document, and that language models tend to favor the start and end of a text. Its advice is to split the document and summarize it in parts. Anthropic's advice for long files is to put the document first and the question at the end, and to ask the assistant to pull out the relevant quotes before answering.

Combining both, our recommendation for any report longer than about 20 pages: summarize section by section, ask for page numbers, then summarize the summaries.

A design studio in Leeds that receives a 60-page tender as a PDF might ask:

```
From the attached tender, list:
- the submission deadline,
- the budget,
- the evaluation criteria and their weights,
- every document we must submit.
Give the page number for each item. If something is not in the
document, write "not stated" instead of guessing.
```

The last line gives the assistant a way out, which Anthropic lists among its techniques to [reduce invented answers](https://platform.claude.com/docs/en/test-and-evaluate/strengthen-guardrails/reduce-hallucinations); it also notes that no technique removes them entirely.

### How to check a summary

Citations make checking possible, not unnecessary. Google says Gemini in Workspace can [make up a source](https://support.google.com/mail/answer/16813283?hl=en) and present it as fact; Microsoft says Copilot in Word does not always cite content from later in a document; OpenAI lists fabricated quotes and references among ChatGPT's possible errors. Four checks before you rely on a summary:

1. Open one citation for each point you will repeat.
2. Compare every number, date, and name with the original.
3. Ask “What did you leave out?” and read the answer.
4. Ask the assistant to review its own summary for accuracy, clarity, and completeness, then to improve it, a three-step sequence Anthropic gives as an example.

### Email threads

Gmail's AI Overview summarizes a thread for all Gmail users, in supported languages; turning off Gmail's smart features also turns off its writing help. In Outlook, Summary by Copilot appears at the top of a thread with numbered citations to each email, and in the new Outlook it can summarize Word, PowerPoint, and PDF attachments. Meetings are another matter, covered in a separate guide of this series.

Before you upload a client contract, check what your plan does with files; a separate guide of this series covers which account to use for confidential documents.

### Keeping documents in one place

If you question the same files every week, put them in a project. See [how projects keep files and instructions together](/guides/ai-at-work/everyday-tasks/projects-and-custom-gpts/).

### When the summary invents something

A wrong detail in a summary is a hallucination like any other. Our page on [checking AI answers](/guides/ai-at-work/everyday-tasks/mistakes-and-hallucinations/) shows what to look for.