.CW file extension
To open .CW files on Windows, install and open CU-Writer for Windows (the application associated with application/prs.cww for .cw/.cww files).
To open a .cw file, use CU-Writer for Windows (the format associated with IANA’s application/prs.cww registration). If you are on macOS, Linux, iOS, or Android, the most reliable approach is to open it on a Windows PC with CU-Writer or transfer the file to someone who has that software.
Last updated: April 30, 2026 · Reviewed by Julian Stricker
Open on your device
Choose your operating system for a dedicated step-by-step opening guide.
How to open .CW files
Use these platform-specific instructions to open .CW files safely.
Windows
- Install and open CU-Writer for Windows (the application associated with application/prs.cww for .cw/.cww files).
- In File Explorer, double-click the .cw file; if it does not open, right-click → Open with → choose CU-Writer.
- If you need to use the file elsewhere, use CU-Writer’s export/save-as features (if available) to create a more widely supported format.
Mac
- There is no commonly supported native macOS app confirmed by the sources for .cw (CU-Writer) files.
- Transfer the .cw file to a Windows PC with CU-Writer installed and open it there.
- If you must work on macOS, ask the sender to export the document from CU-Writer to a more common format first.
Linux
- Your file manager may identify the file as application/prs.cww based on shared-mime-info-style mappings, but that does not guarantee an opener is installed.
- If no compatible application is available, transfer the file to Windows and open it with CU-Writer (the format’s referenced application).
- Keep the original .cw unchanged; request an exported copy from CU-Writer if you need a more portable file.
iOS
- iOS is unlikely to open .cw (CU-Writer) files directly; use the Files app to share/transfer the file to a Windows PC and open it with CU-Writer.
Android
- Android is unlikely to open .cw (CU-Writer) files directly; transfer the file to a Windows PC and open it with CU-Writer.
Security notes
- .cw/.cww is a document format associated with a specific application (CU-Writer); the main practical risk is opening untrusted files in a complex document parser. Prefer opening unknown files in a controlled environment.
- Do not “fix” a .cw file by renaming it to .doc/.docx/.txt—this can lead you to open it with the wrong software and misinterpret content (or trigger unexpected behavior in another parser).
- If a website or email asks you to install unrelated software to open a .cw file, treat that as suspicious; the supported association in the sources is CU-Writer for Windows.
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Can't open this file?
These are the most common causes and fixes when .CW files fail to open.
Common reasons
- Windows shows “Choose an app to open this file”
- The file is identified as application/prs.cww or has the .cww extension
- The file opens but shows garbled text or missing characters
- Linux/macOS cannot find an application to open the file
Fix steps
- Install CU-Writer for Windows, then try opening the file again.
- Right-click the file → Open with → select CU-Writer; optionally set it as the default for .cw files.
OS-specific troubleshooting
What is a .CW file?
.cw (and the related .cww extension) is associated with CU-Writer, a word processor (notably Thai-capable) referenced by the official IANA media type registration for application/prs.cww. The IANA registration lists file extensions cw and cww for that MIME type. Outside CU-Writer, support is not broadly standardized, so the safest expectation is that it is a CU-Writer document/data file.
Background
The most grounded identification for .cw in modern systems comes from the IANA media type application/prs.cww, which explicitly lists the file extensions .cw and .cww and states it is used by CU-Writer for Windows. When a system recognizes the file by MIME type, it may label it as application/prs.cww rather than a generic “CW Data File.”
CU-Writer (also known as Word Chula) is described as a Thai-capable word processor, and .cw/.cww files are associated with documents created by that application. In practical terms, that means typical content is word-processing style document data, and the most reliable way to open it is with the original software.
On Linux and other desktop environments that use the freedesktop.org shared-mime-info system, the extension-to-MIME mapping concept is standard: file managers may associate .cw/.cww with a MIME entry (such as application/prs.cww) and then choose an installed application based on that association. However, the presence of a MIME type does not guarantee you have a program installed that can actually open the file.
If you receive a .cw file and do not know its origin, treat it like a proprietary document: preserve the original, avoid “guessing” by renaming the extension, and use CU-Writer on Windows as the primary route to view or export it into a more common format.
Common MIME types: application/prs.cww
Further reading
Authoritative resources for more details on the .CW format.
Common .CW issues
Windows shows “Choose an app to open this file”
This usually happens when CU-Writer is not installed or the file association for .cw is missing.
- Install CU-Writer for Windows, then try opening the file again.
- Right-click the file → Open with → select CU-Writer; optionally set it as the default for .cw files.
The file is identified as application/prs.cww or has the .cww extension
The IANA registration for application/prs.cww lists both .cw and .cww as associated extensions, so you may see either extension or the MIME type label.
- Try opening it in CU-Writer regardless of whether the extension is .cw or .cww.
- Avoid changing extensions as a “fix”; use CU-Writer to open and then export if you need another format.
The file opens but shows garbled text or missing characters
CU-Writer is a Thai-capable word processor; incorrect fonts/encoding support or opening in non-matching software can lead to unreadable content.
- Open the file in CU-Writer (not a generic editor) to ensure correct rendering.
- If sharing, export from CU-Writer to a more widely supported document format to preserve readability on other systems.
Linux/macOS cannot find an application to open the file
Even if the system can map .cw/.cww to a MIME type, the required application (CU-Writer) is not commonly available on those platforms per the provided sources.
- Move the file to Windows and open it with CU-Writer.
- Ask the sender to export the file from CU-Writer into a more common format.
FAQ
What program opens .cw files?
Based on the official IANA registration for application/prs.cww, .cw (and .cww) files are used by CU-Writer for Windows.
Is .cw the same as .cww?
They are listed together as associated file extensions for the registered MIME type application/prs.cww, and both are used in the CU-Writer context.
Can I open .cw on macOS, Linux, iOS, or Android?
The provided sources only directly associate the format with CU-Writer for Windows. The most reliable workflow is to open it on Windows with CU-Writer or request an exported copy in a more common format.
Should I convert it by changing the extension?
No. Renaming the extension does not convert the file. Open it in CU-Writer and use export/save-as functionality (if available) to create a different format.
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