Working with photography

Question

Hi All,
I often work with images in Illustrator when creating adverts, I know it's not the best programme for this task but I love it and use it for almost everything these days. When working with CMYK document I import a beautiful bright image do the artworking and when I save it as print ready pdf the image looks very dull and flat. Nothing like the original .ai file. I usually edit and export photos from lightroom, I'm not sure if this process is entirely rgb but there must be away to keep photos looking bright and sharp.
Any help would be much appreciated, I've thought this for years now!
Thanks,
Two screenshots, one of the exported pdf (first image) one of the image on an artboard in illustrator (second image).

Answer 1

I almost always open images in Photoshop, convert them to CMYK, then adjust the levels on them after saving them out of lightroom or from any other source.  Jacob is correct in the image overall brightness and saturation becomes a bit dull when converting to CMYK.  Your RGB image is getting converted to CMYK output in Illustrator.  I wouldn't recommend working in RGB in Illustrator unless you are only using it for web content.  The reason being is that blacks that are setup in RGB in Illustrator and then passed on to an offset printer will be converted to process build blacks and printers don't like this at all.    It makes the black type very hard to register on press and it usually ends up making grays come out with some sort of color cast.