With a lot of channels you can imitate a vocoder: You need to split the carrier and modulation signal into frequency bands as Internet Human stated. For each frequency band you need 3 tracks with the exact same filter setup for example for band 1 you chose lowpass at 100 hz and highpass at 50 hz. One channel has the modulator as its input signal, the other to have the carrier signal.
on one of the carrier signals you deploy a compressor and you choose the correlating modulator frequency band channel as a side chain signal in the key in. After the compressor plugin you need to invert the phase of this channel. I think protools eq has a phase invert button which looks like O combined with a /.
The idea of this is to imitate an envelope follower via phase cancelation. No modulation signal -> no gain reduction in the side chain compressor = complete phase cancelation. when gain reduction happens the carrier frequency band is not canceled out completely = you will hear that frequency band respond to the frequency bad of the modulator.
You need to activate delay compensation in protools, else the phase cancelation will not work.