Can I amplify high frequency signal?
If you don't mind being tuned to a single FM frequency, you can use a Class C stage which has a tuned resonant circuit as its load.

A class C stage is very simple because it is not concerned with linearity in the time domain. In fact, the transistor only conducts 50% of the time.

In an instrumentation amplifier or audio, or other such applications, the 
distortion would be unacceptable, but it doesn't matter in RF, because the encoded signal is robust against distortions of the carrier wave.

This is why the approach of using a digital pin is possible in the first place; it doesn't matter that the carrier being modulated is a square wave.

So the answer is yes; you can build an efficient amplifier which amplifies the RF signal and smooths it at the same time.

Look for schematics depicting a "tuned class C RF amplifier stage", or look up the topic in an introductory electronics text.