CMYK is for full colour offset printing (cyan, magenta, yellow, black), like for a magazine or colour newspaper ad. Pantone is for spot colour printing, which is using specialized ink colours for things like merchandise, tshirts, some people's business cards, etc. The two (three including the RGB) are independent of one another and a file set up for one shouldn't be used for the other. This is especially true for corporate applications where company colour matching is imperative. Pantone puts out an extensive line of swatch books for matching RGB, CMYK and PMS to each other on both glossy and matte papers. If you do a lot of design work then they are an excellent resource. If all you had was a PMS logo though, you could convert it to CMYK or RGB, but the results might not be ideal.