There is no such thing as a demo of Krakatoa C4D. If you have an evaluation license, it will be time-limited, but otherwise the same as a full production license.
The most often encountered problem that C4D users seem to report is the difference between the Viewport and the Picture Viewer.
We generally recommend always rendering to Picture Viewer because Krakatoa is heavily dependent on the output resolution, and the Viewport never matches the final resolution. Also, the Gamma (Color Correction) settings of the Viewport and the Picture Viewer are usually different. Just because you don’t see all particles in the rendered image does not mean they were not rendered - they might be just too dark/faint to see.
Can you attach a screenshot of what you see in the Viewport, and the rendered image?
Also, the exact number of particles rendered can be seen in the Script Console window - Krakatoa reports the precise numbers of particles, channels allocated, how long it took to render etc. Does it list the same amount when you render to the Viewport and in the Picture Viewer?