You can convert a book file created in a previous version of InDesign by opening and saving it in InDesign CS3. When you synchronize, update numbering, print, package, or export a converted book, the documents it contains are also converted to InDesign CS3 format. You can decide whether you want to overwrite or keep the original document files.
If you want the original documents to be overwritten during conversion, select Automatic Document Conversion.
If you want to keep the original documents and save the converted documents with new names, deselect Automatic Document Conversion. (The book list will be updated to include the converted files, not the originals.)
Choose Synchronize Book from the Book panel menu. (See Synchronize book documents.)
Choose Update Numbering > Update All Numbers from the Book panel menu.