how to generate a pdf into a file in the server from a link on a web browser

the subject is quite clear...

can somebody tell me how to do it???

since until now i only able to generate the pdf then

view it straight away in the browser

i want to save the pdf automatically instead of

manually save it.

can somebody give me some examples code if you can

save the pdf into file 

the problem is that it take too much in generate, 

and I like to save it intead of generating each time I need it

thanks