Most of the actors read the series, but for some of them it was not completely necessary. For instance, Jim Broadbent (Professor Horace Slughorn) had not read the series befor
…e being cast, only then reading the sixth book, the book that he was introduced. Also, Tom Felton (Draco Malfoy) was cast not having read any of the series either. He went through the first two and a half films not having read the series, but did eventually. He said it was because he wanted to make Draco on his own without being led by the novels. (MORE) 
