The official legal UW is only available online from their website.
However, some folks have copied those questions and answers and put them into word or PDF files or whatever and then they distributed them illegally.
There's a member here who's having it but I don't know who he is.
I don't recommend that you do the offline (illegal) copy of UWorld and the reason is that they constantly update their questions on a weekly basis. They always have new question that reflect the current trend of the exam. So if you get the offline questions (which is usually old, like 2007 or 2008) then you will be missing these updated and new questions.
Also when you do the offline questions you won't get your true percentage and you can't compare your performance to others (both of these features are available in the original online mode).