As Falkyrn says, there is some confusion here between PDFs and Word, never mind RGB and CMYK.
As a long time amateur photographer and serious printer of large photos, plus some lengthy experience in the Print Graphics Industry, I suggest you stay a long way away from CMYK as it will only confuse everything further.
It is true that every colour printer I am aware of actually is a CMYK machine, but they ALL expect RGB input and do the conversion internally. Commercial grade print houses may well transmit CMYK files to their printers but they know what they are doing. The normal user does not.
You need to tell us what the original medium/file type is and how you intend to print it. What is the final output type?? What is that you are trying to do?