What is a .otf file?
OpenType Font · Font · Adobe / Microsoft · 1996
OTF is a modern font format that builds on TrueType with richer typographic features like ligatures, alternate glyphs and advanced spacing. It is a favourite of designers who want fine control over type.
What is a .otf file used for?
OpenType can use either TrueType or Adobe's CFF outlines and adds powerful features: ligatures, small caps, stylistic alternates and support for very large character sets.
It works across Windows, macOS and Linux just like TTF, so which one to choose usually comes down to the specific font's features.
For the web, OTF is again typically converted to WOFF2 for smaller, faster downloads.
What opens a .otf file?
The .otf format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Windows Font Viewer
- FontForge
macOS
- Font Book
- FontForge
Linux
- Font viewer
- FontForge
Web
- Used via @font-face, prefer WOFF2
Open a .otf file step by step
- Confirm the file really is a .otf. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Windows Font Viewer or FontForge.
- On Mac, use Font Book or FontForge.
- On Linux, try Font viewer or FontForge.
- Still stuck? Convert the .otf to TTF, which opens more widely.
Why can't I open my .otf file?
Almost always because no installed app understands OTF. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .otf at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .otf file
You can convert a .otf file to TTF, WOFF, WOFF2 using a conversion tool or the export menu of an app that opens it.
What is the .otf file signature (magic bytes)?
A .otf file starts with the hex bytes 4F 54 54 4F, which read as OTTO in ASCII. Programs identify OTF by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for OTF. For a full breakdown, see the OpenType file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 4F 54 54 4F | 0 | OTTO | 'OTTO' (CFF outlines) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .otf file?
OTF is a modern font format that builds on TrueType with richer typographic features like ligatures, alternate glyphs and advanced spacing. It is a favourite of designers who want fine control over type.
Should I use OTF or TTF?
For everyday use they are interchangeable. Choose OTF when the font offers advanced typography like ligatures and alternates that you want to use.