pedestal fan

Definitely possible. But from where it will suck in the air ?

Normal fans are axial flow fan. ie the air enters and leaves the fan axially. But you will require the fan to suck in air radially now and discharge axially.

You would need a large center tube to supply input air (from between the blades) from below or above. Otherwise you will create a mild vacuum at the motor where a too small supply of air will exist. The fan blades will struggle to turn and will burn the motor out very early.

Without a STRONG central supply, this will be a wasted effort.

I don't normally allow this, but I'm in a good mood so go ahead and have fun.

You certainly can. There are quite a number in use. 2 impellers are used in higher pressure (resistance) applications. For example an induced draft fan on a power plant will have a higher system resistance to overcome with a fabric filter dust collection plant in the system than say an electrostatic precipitator or none at all. Here are 1 and 2 stage fans in similar configuration but they will each have different characteristic curves.

You can mount a second impeller on the other end of your pedestal motor shaft, but you would need to have a reason for it and if you did need it you will need a larger motor.

Hope this helps.