How to Upload .txt, .md, .csv, and .html Files to NotebookLM

TL;DR: NotebookLM accepts text-based file formats as sources, and Kaptex lets you upload them from the browser side panel without navigating away from whatever you're working on.

Why uploading files to NotebookLM takes you out of your workflow

NotebookLM supports file uploads natively, but the workflow requires a few steps each time: go to NotebookLM, open the right notebook, locate the upload option, then find the file on your machine. If you're in the middle of something — coding, reading docs, running analysis — you've now left that context to do an upload manually.

The interruption compounds when you're uploading several files. Developers moving Markdown notes or README files into a research notebook, researchers uploading exported .txt notes from another tool, analysts pulling in CSV data or HTML archives — all of them have to repeat the same trip to NotebookLM for each file. It's not a hard task, but it breaks the flow every single time.

The other issue is that these files don't always come from the browser. They're already sitting on your machine. What's missing is a way to drop them into your notebook from wherever you already are, without the round trip.

How to upload files to NotebookLM with Kaptex

Kaptex adds a file upload section to the side panel, so you can send local files to your notebook without leaving the tab you're on.

Step 1: Install Kaptex and select your notebook

Install Kaptex NotebookLM Extension from the Chrome store and open the side panel.

Select the notebook you want to add files to. The side panel stays open across tabs, so your notebook selection persists as you move around the browser.

Step 2: Open the file upload section in the side panel

In the side panel, find the file upload option. It's a distinct input from the URL and text save options.

Step 3: Select your file

Click the file selector and pick the file from your machine. Accepted formats: .txt, .md, .csv, .html, .htm, .json.

Step 4: Send — the file appears in your notebook

Click send. The file is uploaded to your selected notebook as a source. Switch to NotebookLM and it will be there, ready to query.

What file types work

Each accepted format covers a different use case:

• .txt — plain text exports from note-taking apps, raw transcripts, or any text file you've collected
• .md — Markdown notes, README files, project documentation, or anything written in a docs-as-code workflow
• .csv — data exports from spreadsheets, analytics tools, survey platforms, or any tabular export
• .html / .htm — saved web pages, exported reports, or archived content from tools that export to HTML
• .json — structured data exports from APIs, configuration files, or app data dumps

Developers dropping project docs or README files into a research notebook, researchers uploading .txt exports from their note apps, and analysts working with CSV or JSON exports from data tools are the main cases this covers.

Wrap-up

The file upload in Kaptex's side panel is a direct path from your machine to your notebook — no tab switching, no navigating to NotebookLM, no re-selecting your notebook each time. Pick the file, hit send.

One thing worth noting: NotebookLM also accepts PDFs natively through its own interface. If you're uploading a PDF — including textbooks as PDFs — you'd add those directly through NotebookLM. Kaptex's file upload covers the text-based formats listed above; PDFs go through NotebookLM's own source upload.

You can try it free at kaptex.io — 10 saves per day on the free plan.

Frequently Asked Questions

What file types can you upload to NotebookLM via Kaptex?

Kaptex supports .txt, .md, .csv, .html, .htm, and .json. These are uploaded from the side panel without leaving your current tab. NotebookLM also accepts PDFs and Google Docs through its own native interface.

Does Kaptex support PDF uploads?

No — Kaptex's file upload handles text-based formats only. To add a PDF as a source, use NotebookLM's built-in upload directly. PDFs added through NotebookLM work the same as any other source once they're in your notebook.

Can you upload textbooks to NotebookLM?

Yes, as PDFs via NotebookLM's native upload. Textbook PDFs are processed the same way as any other PDF source, so you can query them, generate study guides, or create audio overviews from them once they're added.

What happens to the file after it's uploaded?

The file is added as a source in your selected NotebookLM notebook. It stays in your notebook as a source you can query, and NotebookLM indexes its contents so you can ask questions about it alongside your other sources.

Is there a file size limit?

Kaptex uploads the file to NotebookLM via its API, so NotebookLM's own source size limits apply. For most text-based files — notes, CSV exports, Markdown docs — size is rarely a concern. Very large CSVs or JSON files may hit limits; if an upload fails, splitting the file into smaller parts and uploading each one separately is the workaround.