12. A non-transitory storage device comprising a program product which allows a computer to realize: using a processor device configured to perform: recognizing speech in a presentation to produce subtitles; extracting keywords from document data used in the presentation; adding the extracted keywords to a voice recognition dictionary; and assigning word attribute weights to the keywords extracted from the presentation based on word attributes read from a word attribute database, wherein said word attributes comprise at least one of: a title, character size, character underlining, and boldface character; recording a time that the page is turned and a time when a next page is turned to determine time spent on the page; storing the time spent as a timestamp; calculating a weight of the keywords on a page based on a combination of: a duration during which said page is displayed in the presentation when it is determined that the extraction of the keyword has been successful; and the word attribute weights assigned to the keywords; a function of determining, among the subtitles obtained by recognizing speech generated with reference to a predetermined document, a specific subtitle obtained by recognizing the speech generated with reference to a specific page of the document; and a function of storing a correspondence between the specific subtitle and the specific page.
14. The program product according to claim 12 , further allowing the computer to realize a function of retrieving character strings, with the retrieval target range extended from the specific subtitle to text data contained in the specific page.