when do i need purchase it?

i know if use a fir ip core, you must purchase it . but if i use a pwm core, whether i don't need to pay money(at lease now there is no any requirement for me to do this) , so i want to check a thing: if the ip core is from ip file(the directory of you install the it), then it need to purchase, other case if it appears in sopc builder, it is free?????

:) sorry for my English ,and sorry for my poor fpga technology. i am a new ,help me:p