Fill Text Box automatically in MSWORD to series number for printing.

I have to print 500 application form made of MS WORD for Computer training Center. Each form has a separete serial no. just like 001,002 within a Text Box. Now I have to change the serial number each time before print one form. But it is very helpful to me if there is any way to automate the serial number in the Text Box and print the form just 1 to 500 easily.
