Mapviewoffile

[DllImport("Kernel32.dll")][return: MarshalAs(UnmanagedType.SysInt)]
public static extern IntPtr MapViewOfFile(IntPtr hFileMappingObject,
   uint dwDesiredAccess,
   uint dwFileOffsetHigh,
   uint dwFileOffsetLow,
   UIntPtr dwNumberOfBytesToMap
);

Microsoft documentation: Link