Getting a HD film on mac harddrive

[sidekickdmr]

Hey all

I need to get 2/3 specific films, in HD, onto my mac to watch offline

I cant work out for the life of me how to do this, even if i buy it on amazon or itunes for a digital copy, it wont let me download it, just "watch" it.

Any ideas please?

happy to pay for the film, and would rather it be legit, just cant find a way!

Thanks