How to convert photos to CMYK?

Are you asking how to convert photos within a PDF file to CMYK? Or are you trying to convert an entire PDF file that may have some RGB content including photographic images to CMYK? Or are you simply trying to use Acrobat to convert RGB TIFF or JPEG photos to CMYK?

If the latter (converting RGB TIFF or JPEG photos to CMYK) is what you are trying to accomplish, all Acrobat Pro would do for you is to convert the images to PDF and within Acrobat you would need to convert the file to CMYK using the Print Production - Convert Colors tool. Then you would need to export to the format you had, TIFF or JPEG. You'd be better off simply opening original file in Photoshop, converting it within Photoshop, and simply resaving the file.

Otherwise, if you already have a PDF file and from that you wish to do conversion, again you should invoke the Print Production - Convert Colors tool in Acrobat Pro, choosing the appropriate option for either converting images or perhaps all content to CMYK. And then save the PDF file.

You should note that you really don't need to convert photos to CMYK in order to print them. If you are dealing with a print professional who still believes in and propagates that mythology, you might want to look for some other printer.

          - Dov