submit button to call pdf file based on the form data

hi, im new to php and Jscript, i did a pdf search function where the user will select the data based on 2 selections and then when he hit the submit button, the button will call a pdf file based on the selections,

my question is how do i tell the submit button to call the pdf file?

example:
user select A from list1 and C from list2, then hit the submit button

results should be:
userdomain.com/pdf/a_C.pdf

i would appreciate anyone can help me to sort this or refer me to any tuts or anything that will get me going on the track

thanks