1. A method comprising: a display step of causing a display device to display a plurality of thumbnail images corresponding to a plurality of images with display items for emphasizing one or more first thumbnail images corresponding to one or more images which have been compressed with a high-compressed PDF, so that each of the display items is added to corresponding one of the first thumbnails and the one or more first thumbnail images are more emphasized than one or more second thumbnail images corresponding to one or more remaining images which have not been compressed with the high-compressed PDF, wherein each of the display items indicates the high-compressed PDF; a selecting step of selecting one or more thumbnail images from the plurality of thumbnail images, in accordance with an instruction from a user; and a generating step of generating a file which includes one or more images corresponding to the one or more thumbnail images selected in the selecting step and corresponds to a high-compressed PDF, by compressing, using a predetermined compression method of the high-compressed PDF, the one or more images which corresponds to the one or more thumbnail images selected in the selecting step and has not been compressed with the high-compressed PDF.