I want to take a look at the PWM Signal (0 - 5 V) of my Arduino project. There are 3 PWM signals I want to see. Is it possible to show the third signal with Channel C or Channel D?
That should be fine. C and D will only show logic levels 0 and 1. Nominally they are for 3.3V logic but they have series resistors and the inputs have clamping diodes so they are OK showing 5V logic.
One thing to be aware of is that the C and D channels on the 2.6 and 2.7 hardware had ESD protection diodes on these channels which had rather high capacitance. This combined with the series resistance meant that the frequency response of C and D was slugged to about 1MHz and there could also be some time offset of a few microseconds with respect to A and B. I believe hardware 2.72 is different in that area as it uses different ESD across all channels. I had one of the earlier models and replaced my ESD diodes with units with much lower capacitance to avoid this limitation.