The feature to generate CMYK TIFF from a PDF needs to be investigated in Aspose.PDF and task has been generated as PDFNET-56237 in our issue tracking system. We will further let you know as soon as the ticket is resolved. Moreover, if you have Aspose.Total or Aspose.Imaging license too, you can use it to convert a RGB TIFF into CMYK TIFF.
The ticket has recently been logged in our issue tracking system and it will be prioritized on a first come first serve basis. As soon as we make some progress towards its resolution, we will inform you via this forum thread. Please spare us some time.