if file reading not possible by userlevel programs how it is doing

the answer is "by help of kernel "

our softwarers are userlevel unprivillaged programs.
the privilage is handled by hardware support, that means it is provided by hardware,

when kernel loads in cpu first it gains higher privillage,
then when we start our software the kernel switch privilage level and runs our software,
then if our software needs file reading like things then we executes systemcalls,
when the system call instrcution is executed by processor the kernals intterupt handler executes ,it is already attached by kernbel when kernel booted, this handler code of kernel runs, and it will now in higher privilage.so kernel then it checks data passed to it (by reading registers )
then by privilaged instructions it reads file,(instructions that is only possible to run when kernel is in higher privillage ),
then file data is returned to userlevel programs,