How to open every TEXT file?

[Yoh-hei]

Hello:
I use VC++6.0 MFC.I have some text file need open
I can open one file the code:
CStdioFile fillnput;
if(fillnput.Open("a:\\Test.txt",
CFile::modeRead|CFile::typeText)){
//Read my file
}
But it's only open one file.
I need open every text file use function OnFileOpen()
(That's said I can select one of files.)
Would you help me?
Welcome any advice!
Thamk you very much.