Is it possible to take individual color separated image files and create a composite CMYK pdf using PDFTron?
You could either extract just the image data from each page and make 4/5 channel image, where each page is the corresponding channel, and then make a new PDF page with that image.
Or if you also want the vector content that surrounds the image, then you could use our SDK to raster the entire page, and then repeat the step above.
Is that what you are looking to do?