ClarisWorks / AppleWorks Document (.cwk)
The CWK file extension stands for ClarisWorks Document, specifically used for word processing documents within ClarisWorks (later AppleWorks). Apple rebranded ClarisWorks to AppleWorks after acquiring Claris in 1998 and discontinued it in 2004. These CWK files have since been largely replaced by formats like PAGES in Apple's iWork suite. Opening CWK word processing files now requires older versions of Apple's Pages.