PDF (adobe.com)

Importing DCS files

Desktop Color Separation (DCS) is a version of the standard EPS format. The DCS 1.0 format supports only CMYK images while the DCS 2.0 format supports multichannel CMYK files as well as multiple spot inks. (These spot inks appear as spot colors in Illustrator’s Swatches panel.) Illustrator recognizes clipping paths in Photoshop-created DCS 1.0 and DCS 2.0 files. You can link DCS files in Illustrator, but you can’t embed or open them.

To see DCS transparency interactions in the Links panel, choose Panel Options from the Links panel menu and select Show DCS Transparency Interactions.