ascii keyboard input

Is it possible to enter keystroke on the PC and read them realtime into the Arduino.

I did some searches, but didn't find what I needed.

Sure - fire up the serial monitor, send them to the arduino over the USB port.

You can read it in, send it right back.
This assume you have USB cable between PC & Arduino for example:

    int inByte = 0;
void setup(){
  Serial.begin(57600);  // set serial monitor to same speed
}
void loop(){
  // read from port 0, send to port 0:
  if (Serial.available()>0) {  // check if any data received
    inByte = Serial.read(); // yes, so read it from incoming buffer
    Serial.print(inByte, BYTE);  // now write it out the serial port
  }
} // back to the top ...

Is it possible to enter keystroke on the PC and read them realtime

If you mean "as they are pressed", then no, the serial monitor isn't for you.
It only sends the string you typed in when you hit the send button.
But any terminal emulator that can connect to a serial port will do the trick.

But any terminal emulator that can connect to a serial port will do the trick.

or investigate Processing to make yourself a window to type things in.