Luke - 18 minutes ago »
Not always. Even in properties this can show up as "hdr_foxt2_upgrade.hdf" even when it is "hdr_foxt2_upgrade.hdf.hdf" if the PC thinks it recognises "hdf".
You could simply ask the OP if he manually added .hdf at the end of the file extracted from the archive and if the original file had no extension at all.