StgOpenStorage

[DllImport("ole32.dll", SetLastError = true)]
public static extern int StgOpenStorage(
   [MarshalAs(UnmanagedType.LPWStr)] string pwcsName,
   IStorage pstgPriority,
   uint grfMode,
   IntPtr snbExclude,
   uint reserved,
   out IStorage ppstgOpen
);

Microsoft documentation: Link