searching for text in a mixed file (text and hex)

I have the following code below to take a selected file and read it's
contents.
The app has a ListBox (IDC_FILELIST) and Static text (IDC_FILESELECTED).
More will be added later to process the read file.
How do I search for a text string when the file does contain 0x00's in it.
It is a mixed file containing text and hex data?
I compile with no errors and the filename does appear at IDC_FILESELECTED.

Please feel free to direct me in other things I am doing improperly.

BOOL CMyAppDlg::OnInitDialog()
{
  CDialog::OnInitDialog();

  SetIcon(m_hIcon, TRUE); // Set big icon
  SetIcon(m_hIcon, FALSE); // Set small icon

  CListBox* List = (CListBox*)GetDlgItem(IDC_FILELIST);
  List->ResetContent();
  HANDLE hand;
  WIN32_FIND_DATA tell;
  CString William = "C:\\temp\\*.ppf"; //file I am listing have a .ppf
extension

  LPCTSTR Ppath = William;
  CString insert;

  hand=FindFirstFile (Ppath, &tell);
  if (hand != INVALID_HANDLE_VALUE){
    insert = tell.cFileName;
    List->AddString(insert);
  }
Search:
  if (FindNextFile(hand, &tell)){
    insert = tell.cFileName;
    List->AddString(insert);
    goto Search;
  }
  UpdateData(false);

  return TRUE;
}

void CMyAppDlg::OnSelchangeFilelist()
{
  char cSelect[500];
  int nSelect;
  long lth;
  FILE *in;

  nSelect=SendDlgItemMessage(IDC_FILELIST, LB_GETCURSEL, 0, 0L);
  DlgDirSelect((LPSTR) cSelect, IDC_FILELIST);
  GetDlgItem(IDC_FILESELECTED)->SetWindowText(cSelect);
  UpdateWindow();
  Fname = "C:\\temp\\"; //set directory path
  Fname += cSelect; //append filename selected
  in = fopen (Fname, "rb"); //open the selected file for binary
reading
  fseek(in, 0, SEEK_END); //Move File Pointer to EOF
  lth = ftell(in); //Get position of FP
  fseek(in, 0, SEEK_SET); //Move FP back to beginning of file
 edi = new TCHAR[lth]; //create place for data (declared
"LPTSTR edi;" in header file
  fread (edi, lth, 1, in); //read entire file into edi
  fclose (in);
 fileSize = (int)lth; //save the filelength for future use

}