in mach 3 can i use serial port and connect it with plc and take the output to certain address and then control the machine from it and also if this possible can also i input some data from plc to mach 3
all the best

If your PLC has serial ModBUS then you can communicate with Mach for general I/O, time critical things such as axis control is a different matter.
Hood

thanks but that's main axis control should be with parallel port can u tell me what's happen if i connect axis also through parallel port

thanks but that's main axis control should be with parallel port can u tell me what's happen if i connect axis also through serial  port

As far as I know the serial port is not good enough for time critical things such as motion control, you could possibly manage with the high speed addons for the PLC for controlling motors but really that would start to get expensive and very complex. It is  way above my head.
Hood