save() function in javascript by default saves the file as ai

Hi,

I am using save() function in Illustrator to save the opened file. I am having the PDF file opened in my Illustrator if there is any modifications in file then want to save the file as pdf only but if i use the  save() API  then it saves the file as ai.

Example:  app.activedocument.save()  //here my activedocument is .pdf file.

Is there any way to save the file in opened format only.?

Thanks,

Yogita