Assuming that the processor is a CMOS chip powered from 5V, the highest voltage any port pin will pull to while sourcing a couple of mA to the base of the NPN through R4 is about 4.8V. R4 is not needed, so leave it out.
You will loose another 0.7V as the base-to-emitter drop on the '3904, so the highest voltage you will ever get to pin 4 of HC-12 will be 4.8V - 0.7V = 4.1V. Is that enough? Probably not!
How much current does the HC-12 require? At what voltage?
The correct approach is to use a "high side PMOS" switch circuit. Can you reverse the logic on the port pin such that it is "low" when you want the HC-12 to be powered?