Reply To: Export images as grayscale to PDF while preserving spot color?

I don’t know of a means in ID. You can use Acrobat, Tools, Convert Colors, though. You would set the drop down in the Matching Criteria section for Object Type to Image. Then on the right-hand side, Convert to Profile, Conversion Profile would be set to your choice of installed grayscale profiles.

Try on a copy of your PDF and check using Acrobat’s Preflight Profiles to make sure the Pantone is untouched and the images are gray.

Mike