1. An information processing apparatus comprising: a memory; and a processor, which: receives instructions from a user to search for a document; searches for the document in a storage associated with the information processing apparatus; stores the document in the memory; classifies the document into a first category and a second category; extracts a word from the document; determines a first total number of documents in the first category; determines a second total number of documents in the second category; determines a first number of documents as a first count of the documents in the first category that contain the word; determines a second number of the documents as a second count of the documents in the second category that contain the word; determines a first ratio of the first total number of documents and the first number of documents; determines a second ratio of the second total number of documents and the second number of documents; calculates a word score for the word using a mathematical product of the first ratio and the second ratio, wherein the word score is higher when the word appears less frequently in the category; extracts a sentence from the document; calculates a sentence score for the sentence on the basis of the word score; and displays the sentence on a display, when the sentence score exceeds a threshold.