Files with the .CRD extension contain information such as names, addresses, telephone numbers, and digital signatures identifying persons or companies. The files are created by the Windows CardSpace application which is used to manage digital identities. Windows systems before Windows 95 also used CRD - but it was a different format, and today can be operated using the AZZ Cardfile software. CardSpace technology ceased to be provided by Windows in 2011.

CRD cards enabled users to have a virtual ID used to log on securely to a large number of websites that supported the technology, as well as to company websites thanks to IDs issued by the company or organizational bodies. Authentication usually involved only the transmission of a digital signature, without transmitting other identification data.