Document classification/categorization is a problem in information science. The task is to assign an electronic document to one or more categories, based on its contents [Wikipedia].
Sentiment analysis refers to a broad area of natural language processing, computational linguistics and text mining. Generally speaking, it aims to determine the attitude of a speaker or a writer with respect to some topic. The attitude may be their judgment or evaluation (see appraisal theory), their affective state (that is to say, the emotional state of the author when writing) or the intended emotional communication (that is to say, the emotional effect the author wishes to have on the reader) [Wikipedia].