What is a .one file in OneNote?
A .one file is one section of a OneNote notebook, holding the pages of that section. Microsoft documents the format as the OneNote Revision Store File Format, and NotePeek opens .one files on Windows without OneNote.
What is inside a .one file
Microsoft documents the format as the OneNote Revision Store File Format, which covers .one and .onetoc2 files. You can read the specification on the Microsoft Learn site.
It is a binary format, built from object spaces and a transaction log. A text editor therefore shows mostly unreadable bytes, not your notes as you wrote them. If you want to read what is in the file, you need a program that understands the format.
How a OneNote notebook is stored
A notebook is a folder of section files.
If you are moving or backing up a notebook, keep the whole folder together so that no section is left behind.
How to open a .one file without OneNote
NotePeek: open .one files without OneNote
NotePeek opens .one and .onenote section files on Windows without OneNote. It shows text, images and tables, copies the text of a page and exports the section text as a .txt file. Your files are read on your PC and nothing is uploaded.
NotePeek does not show handwritten ink, and the page tells you so. Attachments are listed by name but not opened. If a section relies on ink or on attached files, you will not see the ink or the contents of the attachments.
NotePeek opens .one section files, not .onetoc2 files. If you only have a .onetoc2 file, NotePeek will not open it, so look for the .one section files instead.
OneNote for Windows 10 and your old notes
OneNote for Windows 10 reached end of support on October 14, 2025. Microsoft says it is now read-only, and viewing and exporting still work. The details are on the Microsoft support page.
If your old notes live in that app, you can still view them and export them, so export a copy of anything important. Because the app is read-only, you cannot add or change notes there, so a notebook you still need to edit has to be opened in an app that allows editing.
Frequently asked questions
What is a .one file?
A .one file is one section of a OneNote notebook, holding the pages of that section. A notebook is a folder of section files.
Can I open a .one file without OneNote?
Yes. NotePeek opens .one section files on Windows without OneNote. It shows text, images and tables, but not handwritten ink, and it lists attachments by name without opening them.
Can I read a .one file in a text editor?
No, not in a useful way. Microsoft documents the format as a binary format built from object spaces and a transaction log, so a text editor shows mostly unreadable bytes, not your notes as you wrote them.
Does OneNote for Windows 10 still open .one files?
OneNote for Windows 10 reached end of support on October 14, 2025. Microsoft says it is now read-only, and viewing and exporting still work.