printDownloadlink is a function provided by the download list plugin and of course does not exist in your theme if not already used. None of the official themes does use it by default. Same for the unprotectedFUllimageurl. You don't need to know where these functions are defined. You need to add/use them where applicable. Where that is is your decision.
I really recommend to read the theming tutorial to learn the basics (html and basic php knowledge not avoidable) before trying to modify or do anything on a theme.
