An information processor for preventing information contained in a file, which has a first area storing first data, a second area storing second data and a third area, from being lost when a format of the file is transformed includes extension unit for extending the second area, a first storage for storing the first data, which is stored in the first area, in the third area, a format analyzer for reconstructing the second data stored in the second area on the basis of a first format and an extended area storage for storing the reconstructed second data in the extended second area.