CreateFileMapping

[DllImport("Kernel32.dll")][return: MarshalAs(UnmanagedType.SafeHandle)]
public static extern SafeFileHandle CreateFileMapping(
   IntPtr hFile,
   IntPtr lpFileMappingAttributes,
   uint flProtect,
   uint dwMaximumSizeHigh,
   uint dwMaximumSizeLow,
   string lpName
);

Microsoft documentation: Link