Try flattening a "copy" of the original, in the copy assign or apply an Adobe RGB profile to it. In your Color Settings, honor profiles when converting to CMYK in order to maximize the conversion gamut. I believe you can still adjust the image in the PDF format as suggested already.
When you go to save your AI file as a PDF, click on the the “Output” tab in the window that pops up. There will be different options concerning Color Management. Under “Color Conversion,” select “No Conversion.”. And then with ”Color Profiles,” select ”Include All Profiles.”. This will prevent AI from converting yourAbout "Rich Black": It's become common to misuse the term "rich black" when referring to black that was intended to be 100%K, but somehow inadvertently entered the realm of RGB at some point, and is now reconverted to CMYK with values something like 69.5%C, 67.2%M, 63.7%Y, 73.8%K. This is not rich black.Select the object or image you want to convert. Go to Edit > Edit Colors > Convert to RGB. The object or image will now be in RGB color mode. Additional Tips: You can also convert an entire CMYK. The CMYK color model is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four ink plates used in some color printing: cyan, magenta, yellow, and key (black). a3zBHU.