pinMode(txPin, OUTPUT); //pin 6
pinMode(rxPin, INPUT); //pin 8
You told SoftwareSerial that these were it's pins. Why are you now diddling with them?
What, exactly, did you connect between the Arduino and the RFID reader? Show a picture.
A status/error byte and a varying number of
data bytes will be returned depending on the command called.
Why don't you read this data?