What is the CPK file format?
The .cpk file extension is used by log packages created by Driver Test Manager (DTM), a tool included in Microsoft's device certification software suite, the Windows Logo Kit (WLK). A .cpk log file stores a complete testing report that captures all information about a tested hardware device. The test log package generated by DTM is saved as a compressed archive, bundling test run data, parameters, and pass/fail results into a single portable file.
Two uses of .cpk files
The .cpk format was developed with two goals in mind: sending generated test reports to Microsoft for Windows hardware certification, and debugging failed tests. Because the package is compressed, large test runs stay portable for submission through tools such as the legacy Microsoft Winqual Submission Tool.
Browsing .cpk files
Information in .cpk files can be accessed using the DTM Log Viewer tool. The application displays test information such as operating system, test date, and passed and failed test cases. Related output in the certification workflow may also appear as .ETL event traces, .LOG text files, or .CAB cabinet archives. The legacy DTM/WLK toolchain has since been superseded by the Windows Hardware Lab Kit (HLK) and its own log formats.
Note: the .cpk extension is also used by an entirely separate format - CRI Middleware's game asset package, common in Japanese console titles. The DTM context (device certification environment, Windows hardware testing) is the only reliable way to tell the two apart.
Security & safety
RISK: LOWA Microsoft DTM .cpk is internal test-log data with no executable payload, so the file itself is low-risk. The practical caution is identification: most .cpk files online are CRI game-asset archives (often from ripped games - see also_used_by), not Microsoft logs, so confirm what you actually have before searching for tools. Avoid sketchy 'CPK opener' download sites that bundle adware; use the DTM Log Viewer for genuine certification logs.
Format details
in a nutshell- CRI Middleware CPK package (games) - By far the most common .cpk in the wild: a CRIWARE data archive bundling game assets (audio/video/files). Extract with CRI Packed File Maker tools or community tools like YACpkTool/CriPakTools - a completely different format.
- Colorimetry / monitor calibration (.cpk) - Some calibration and other niche applications reuse .cpk for their own package/profile data; identify by the creating application.
Programs that open CPK files
Windows3 apps
DTM Log Viewer
Built-in Open the .cpk in the DTM Log Viewer (part of the Windows Logo/Hardware Certification Kit) to read the test run and results. 
Microsoft Winqual Submission Tool (legacy)
Built-in Legacy tool in the certification workflow that handles DTM result packages for submission. Obsolete - kept for historical context.
Windows Hardware Lab Kit (HLK) Studio
Built-in Modern successor to DTM/WLK; use HLK for current hardware certification (it does not open legacy CPK directly but is the current toolchain). Technical details
deep spec| Developer | Microsoft Corporation |
| Format type | Proprietary compressed log package (binary container) |
| Encoding | Binary; exact internal layout not publicly documented |
| Compression | Compressed archive (Microsoft describes the CPK as a compressed log file; specific algorithm not publicly specified) |
| Encryption | None documented |
| MIME type | application/octet-stream |
| File identification | No documented magic bytes; identified by the `.cpk` extension and DTM/WLK toolchain context |
| Typical file size | Hundreds of KB to tens of MB, depending on the scope of the test run captured |
| Structure | Compressed package bundling a hardware device's DTM/WLK test run: tests performed, parameters, and pass/fail results |
| Primary viewer | DTM Log Viewer (shows OS, test date, and pass/fail test cases); Windows HLK Studio for newer certification runs |
| Associated OS | Windows (DTM/WLK and HLK device-certification environments) |
| Superseded by | Windows Hardware Lab Kit (HLK) and its own log and package formats |
| Extension collision | The `.cpk` extension is also used by CRI Middleware game asset packages - an entirely unrelated format from the games industry |
| Submission workflow | Packages submitted to Microsoft for Windows hardware certification via the Winqual Submission Tool |
| Released | 2000s (Microsoft DTM, part of the Windows Logo/Hardware Certification Kit - WLK/HCK) |
| Latest version | Tied to the legacy DTM/WLK toolset (superseded by the Windows HLK); no public format versioning |
| Specification | learn.microsoft.com |
CPK conversions
Community Q&A
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