Original files that are to be archived or shared, need to be supplemented with versions in persistent formats. If you, for example, want to archive spreadheets created in Excel, it is advisable to save these as xcl-files with all content (such as graphs or formulas), and as cvs-files combined with a good description (attached in a pdf) of how the graphs or formulas were made. In using this method, you ensure that there is a specific and persistent format available.