EMF (acronym for Enhanced Metafile Format) is a graphics format that incorporates both vector graphics and bitmap elements. EMF is in fact a 32-bit variant of the WMF format (Windows Metafile Format) that only has support for 16-bit data.
EMF image files do not support CMYK (Cyan Magenta Yellow Black) data but allow users to save image data in RGB (Red Green Blue).
In order to adjust their EMF images, users will have to choose and use a graphics editor that features support for this particular image format.