Files with the .CPK extension contain data such as test data, test operating system, and information concerning successful and unsuccessful test attempts. The files are part of Windows device driver test reports.

CPK log files are created by the Driver Test Manager software, or DTM for short, which is part of the Microsoft device certification suite, also known as the Windows Log Kit, or WLK for short. CPK files are used for transferring device test results to Microsoft for the purposes of certification of the given device for application in Windows. The files can also be used to debug failed tests. Microsoft’s Windows Hardware Quality Labs group, or WHQL for short, is the entity responsible for hardware certification and is also the publisher of the WLK software.