Let me be clear as possible.
You Galaxy S5 G900F DOES SUPPORT 4G LTE. Congrats and it's an international version which will work fine in Pakistan.
Now coming at your problem. For you to enable 4G LTE you have to update the firmware. Firmware is a software which enables operating system to interact with hardware. Now your hardware is supported but sadly your firmware isn't which in turn isn't showing LTE Modes at operating system level. This is because your ROM(firmware) is carrier based.
Now you need to install an international ROM which will enable you to access LTE bands. Which will void your warranty.
If there is some other way like secret codes to enable, I will let you know very soon.