Merge Files in C#.net

These functions are merged a files in the Folder from One location to another location.

public  void mergefiles(string inputFile, string outputFileName)
            {
                #region get PCL file from inputFile
                string[] tmpfiles = Directory.GetFiles(inputFile, "*.pcl");
                #endregion get PCL file from inputFile
                FileStream output = new FileStream(outputFileName, FileMode.Create);
                 #region start Processing 
                foreach (string tempInput in tmpfiles)
                {
                   FileStream inputfiles = new FileStream(tempInput, FileMode.Open);
                    CopyStream(output, inputfiles);
                }
                #endregion start Processing

                MessageBox.Show("Done");

            }

void CopyStream(Stream destination, Stream source)
        {
            int count;
            byte[] buffer = new byte[BUFFER_SIZE];

            while ((count = source.Read(buffer, 0, buffer.Length)) > 0)
                destination.Write(buffer, 0, count);
        }