Thanks for your reply, Paul C
I really appreciate this.
.wdt format, I think it stands for "waveform data type". I am having NI ELVIS and there's a application called "Arbitrary Waveform Generator" and it takes such kind of file format. Finally I found I could use one program came with NI ELVIS as well, called Waveform Editor, to edit some waveform I would like to use. All I have is only an ELVIS and my laptop installed LabVIEW. Thanks for your suggestion to look at DAQmx vi example. I will take a look at it. Thank you again!
NANONFSMW