We are unable to open the DXF files. Could you please advise which program to use to open these files?

There are equivalent PDF files for each of the DXFs, so you are not missing out if you cannot open the DXF. However, the DXF files are 2D scaled drawings that are often used by laser and profile cutters. If you wish to view these files you would need to download a (free) DXF viewer such as DWG Tueview