* Works only in file formats that's supports CMYK like tiff, jpg and etc.
* Tip: Saving the file under CMYK may cause some color tints to change when re-open the file. Therefore it is a good idea to keep a copy of the original file in case you'll re-need it.

Saving your file in CMYK is very simple:
1) Open the desired file
2) Click on the File -> Save As... menu
3) On the Save As dialog select file format that supports CMYK like "JPEG/JPG" from the "Save as type" list.
4) Click on the advanced button and select CMYK from the photometric list.
5) Click OK to confrim and close the advanced box, next click Save to finish.