Copies a specified number of bytes from the current seek pointer in the stream to the current seek pointer in another stream.
pstm Reference to the destination stream. cb The number of bytes to copy from the source stream. pcbRead On successful return, contains the actual number of bytes read from the source. pcbWritten On successful return, contains the actual number of bytes written to the destination.
For more information, please see the existing documentation for IStream::CopyTo in the MSDN library.