First of you need to look at which bands are used in your country and compare them to the Verizon bands. Which can be found on google as I cannot link to other websites . Most countries outside of the US have carriers that use GSM networks so beware as verizon does not and uses a CDMA network. If you have a carrier in pakistan that uses GSM bands you can look at buying an AT&T version and look if bands coincide.
I would also suggest buying a unlocked phone which would make things much easier, as some custom roms cannot be flashed on the verizon/sprint version. If you want to flash custom roms you do need to unlock the bootloader. As I said above GPE roms usually do not work with verizon/sprint edition of a phone, as far as I know you can flash a GPE rom from phones on other carriers. Still I heavily suggest buying an unlocked phone.
I myself am using an unlocked HTC One M8 and have found no bugs whatoever and use a GPE rom and everything is smooth as silk. It's an amazing phone and worth the last penny but if your phone won't work with the bands in your country it's useless so be carefull!