Express entry is not a program itself, rather just a first step filtering scheme for who can apply. You still have to meet requirements for one of the 3 PR programs, either FSW, CEC or PNP.
You either have to qualify FSW (federal skilled worker) which requires you to have minimum one year of full time experience in the same profession / NOC (though you might have that experience before your masters in say Pakistan assuming you worked after bachelors for at least a year)
OR you might need to have one year of full time experience in the same NOC IN CANADA to qualify CEC.
If you have neither, unfortunately you cannot apply for PR yet irrespective of whatever points you have.
Beyond that, if you apply from Canada, then you can extend your status there i.e. being on a PGWP and if its expiring, you can get a BOWP to continue living in Canada while your PR processes.
You cannot get extension if you apply for PR from outside Canada.
Whatever you do don't change your location in the middle of process i.e. if you apply from Canada - stay there until your PR concludes (short visits are fine, i am referring to living for longer periods)
Or apply now from Pakistan and then move back to Canada continuing to work on your PGWP - Don't do this either