What is the ONE file format?
A .one file is a Microsoft OneNote section - the fundamental unit of content storage in a OneNote notebook. Each notebook is made up of one or more .one sections held together by a companion .onetoc2 table-of-contents file. When a notebook needs to be shared as a single portable archive, OneNote packages those files into a .onepkg bundle.
Internally, .one uses the binary MS-ONESTORE format - a proprietary object graph composed of File Node Lists. Every page, paragraph, ink stroke, image, and embedded attachment is stored as a typed node within this revision-aware graph, which enables efficient incremental sync across devices via OneDrive without re-uploading entire sections.
A .one section can contain:
- Formatted text, outlines, and tables
- Handwritten ink strokes with pressure metadata
- Embedded images, audio clips, and video
- Arbitrary file attachments stored inline
- Tags, hyperlinks, and mathematical equations
The format begins with a 16-byte GUID signature (E4 52 5C 7B 8C D8 A7 4D AE B1 53 78 D0 29 96 D3) at offset 0, which file-identification tools use to confirm the type. Individual page objects carry CRC-32 checksums for integrity checking.
Password-protected sections apply AES-128 encryption to their content while leaving the file header unencrypted. Microsoft published the MS-ONESTORE specification, making the format partially open and accessible to third-party converters and viewers.
Security & safety
RISK: LOWA .one file is OneNote note data and isn't an executable, so opening one in OneNote is safe. The realistic risks are indirect: (1) notes can EMBED file attachments, so an .one from an untrusted source could contain a malicious attachment you launch from within the notes - let antivirus scan attachments before opening them; (2) when using third-party online OneNote viewers/converters, don't upload confidential notes. There have been past Office/OneNote security issues (e.g. OneNote attachments used in 2023 phishing campaigns), so keep OneNote updated and be cautious with notebooks/attachments from unknown senders.
Format details
in a nutshell- 1-2-3 / generic data (rare) - A few legacy tools have used .one for unrelated data; the OneNote section meaning dominates overwhelmingly today.
Programs that open ONE files
Windows3 apps
Microsoft OneNote (desktop app)
Free Open OneNote, File > Open, browse to the .one (or double-click). The free desktop OneNote is the primary tool; for a whole notebook open the .onepkg.
OneNote for the web
Free If the notebook is on OneDrive, open it in a browser at onenote.com - no install needed. (Loose local .one files must be added to OneDrive first.)
Free OneNote viewer (e.g. BitRecover/Turgs)
Free Open and read .one/.onepkg without OneNote installed; useful for recovery/preview (read-only). 
macOS1 app
OneNote for Mac
Free Install the free OneNote from the Mac App Store; open notebooks via OneDrive. Loose .one/.onepkg from Windows may need importing through a OneDrive-synced notebook. 
Android1 app
OneNote for Android
Free Free app; opens your OneDrive notebooks. Sign in to access synced sections.
OneNote for iOS
Free Free app; opens notebooks synced from your Microsoft/OneDrive account (not loose local .one files).
Online OneNote viewer/converter
Free Upload a .one to preview or convert to PDF/DOCX in the browser without OneNote (don't upload confidential notes to third-party sites). Technical details
deep spec| Format type | Binary container using the MS-ONESTORE object graph (not XML or ZIP-based) |
| File signature (magic bytes) | 16-byte GUID E4 52 5C 7B 8C D8 A7 4D AE B1 53 78 D0 29 96 D3 at offset 0 |
| MIME type | application/onenote |
| Internal structure | File Node List - chunk-based, extendable layout with a revision graph tracking all edits |
| Content types stored | Text, tables, digital ink strokes, images, audio clips, video, embedded file attachments, hyperlinks, tags |
| Handwriting support | Ink strokes stored as vector paths with per-point pressure and tilt metadata |
| Sync model | Revision-aware incremental sync; only changed chunks are transmitted to OneDrive |
| Integrity checking | CRC-32 checksum per page object for detecting corruption |
| Encryption | AES-128 section-level password protection; file header remains unencrypted |
| Text encoding | Internal strings stored as UTF-16 LE |
| Companion files | .onetoc2 (notebook table of contents linking sections), .onepkg (portable notebook archive) |
| Developer | Microsoft |
| Platform support | Windows, macOS, iOS, Android, and browser via OneNote for the web |
| Spec availability | Documented under MS-ONESTORE and MS-ONE in Microsoft's Open Specification programme |
| Embedded attachments | Arbitrary binary files can be embedded inline within a page node, stored as opaque blobs |
| Released | OneNote 2003; current .one binary format since OneNote 2010 (MS-ONE/MS-ONESTORE published) |
| Open standard | Yes · royalty-free |
| Specification | learn.microsoft.com |
ONE conversions
Community Q&A
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