Please can someone help me.

Im setting up new drawing templates for our new interior design business.  I have both stb and ctb files in my plotter folder but I can't open/utilise any of the ctb files.....therefore when I try to plot to pdf and choose grayscale, it plots in colour 

I have never done this before so need simple step by step advice

I understand that I need to convert the drawing to ctb but previous advice using COVERTPSTYLES is not working

Im on 2017 on MAC