add "get pdf" button

I’m dealing with pages that will be used by teachers to provide their assignments to students in a senior college. Their assignments contain links to PDFs. Is there any button that allows one to choose to “get Adobe reader” button (doesn’t have to be Adobe) like there used to be, or in general is reading a pdf now a function of the browser? IF so can anyone point me to a general instruction sheet describing how to set the browser in the various operating systems? Thanks!