As of yesterday I cannot download pdf files. Instead I get a pop up box that says CONVERT and gives me dozens of programs. How do I just download without this box stopping me?

i click on any pdf file and instead of it just downloading and opening automatically as it has always done - instead it shows the download box and then another pops up titled CONVERT and then gives me a million different options - word / excel / every version of every one! DOS. even if i pick one it comes up in computer language. As of 2 days ago it worked properly and in Safari or another program I can open the pdf. What's happening? HELP