Can i use PL2303 USB to TTL Serial Converter Module send keystrokes using Arduino nano?
No. That is serial. Just like every other USB to TTL Serial converter. The clue is in the name.
You need an Arduino with a dedicated native USB interface, like those based on the ATMega32U4 chip.
Or dedicated software on the PC that will read serial data and emulate keypresses (which is outside the scope of this website).