The cfile tag should be used for questions about the CFile and CStdioFile classes (and their relatives) in MFC (Microsoft Foundation Classes) for C++ code. You should normally add the C++ (or possibly Visual-C++) and MFC tags too. It is not appropriate for questions tagged C — use the plain 'file' as the tag for such questions.
See CFile class and CStdioFile class on the Microsoft Documentation site for two primary references.
