Two simple litte buttons: forward and backward. As in: go to the next file in the current folder or to the file before the current one. I don't mean a history-based function; just two buttons to browse through the current folder without having to use the file open dialog. A prior viewer we used (that had a helluva lot more filetype ability) had this function and it turned out to be very handy.
KState92 Inventor Professional 2014 64 SP1 Windows 7 64 bit - SP1 Xeon E5-1620 16 GB Ram Quadro 4000