Thank!!, I add this to complete the process...

Local lcFileName
lcFileName = Getfile("txt", ;
this.Caption, ;
"Escojer ..")

If Empty(lcFileName)
Return
Endif


Yournewfilename=chrtran(lcFileName,' ','_')

RENAME [&lcFileName] TO [&Yournewfilename]
lcFileName = Yournewfilename




>>Hi if I have a file named [file test.txt] how can replace by [file_test.txt]
>>
>>thank
>
>

Yournewfilename=chrtran(youroldfile,' ','_')