On behalf of Adobe ...
Adobe applications including InDesign, Illustrator, and Photoshop intentionally omitted the capability of initiating a pre-separated PDF workflow. Although one could hack together a pre-separated PDF file by producing PDF via distillation of PostScript (another workflow that we at Adobe most strongly discourage), the concept behind modern PDF publishing workflows is to leave final form content at the highest level of abstraction until it needs to be rendered, whether that rendering is on screen (an inherently RGB device), to 4 colorant CMYK process printing, or high fidelity printing using traditional CMYK colorants plus other colorants such as bright green and orange or light cyan and light magenta as well.
Once you pre-separate PDF, you can't really display the PDF for normal reading, you can't readily search and/or touch up, and you can't change the target printing condition. You also cannot have live transparency in a pre-separated PDF file! And modern native PDF RIPs don't work with such workflows! No ISO PDF/X standard supports such workflows either!
You want or need to preview the separations? Use the separation preview feature of Acrobat (or even the authoring applications).
If you are working with a Luddite print service provider who demands such PDF files or creates them internally, you really need to very seriously consider other print service providers.
- Dov