How to open a .one file (Windows, Mac, Linux)

Q: Why can't I open my .one file?

Usually your computer lacks an app that understands OneNote. Install one of the apps listed here, or convert the file to a more common format.

A .one file is a Microsoft OneNote Section File. If double-clicking does nothing, your computer simply does not have an app that reads OneNote yet. Here is how to fix that on each operating system, using free software wherever possible.

Open a .one file step by step

Confirm the file really is a .one. Drop it into the WhatFileType file identifier, which reads its signature without uploading anything.
On Windows, open it with Microsoft OneNote or OneNote for the web (after import).
On Mac, use Microsoft OneNote (import) or OneNote for the web.
On Linux, try OneNote for the web (after import to OneDrive).
Still stuck? Convert the .one to pdf, which opens more widely.

Best apps to open .one files

Windows

Microsoft OneNote
OneNote for the web (after import)

macOS

Microsoft OneNote (import)
OneNote for the web

Linux

OneNote for the web (after import to OneDrive)

Before you open it: Mostly safe. A .one file is a note store, but sections can contain embedded file attachments; treat attachments inside notes from strangers like any other download.

Frequently asked questions

Why can't I open my .one file?

Almost always because no installed app understands OneNote. Install one of the apps above, or convert the file to a format your existing software already reads.

How do I open a .one file?

In OneNote on Windows use File > Open and pick the file, or place it back in its notebook folder. On other platforms, import the notebook into OneDrive and open it with OneNote for the web.

What is the difference between .one and .onetoc2?

Each .one file is one section of a notebook; the .onetoc2 file is the notebook's table of contents that tells OneNote which sections belong together and in what order.