Is it permissible to give a percentage of the profit to someone who guided me to a job in a company where he does not work?

What your friend does, mediating between you and companies, is called "brokerage" (samsarah). This is permissible in Islamic law and falls under the category of "ju'alah" (a stipulated reward for performing a task). It is a condition that the broker's fee must be known. The majority of jurists have held that it is impermissible for the fee to be a percentage of the profit, because it would then be a ju'alah with an unknown reward. However, some scholars have permitted the fee to be a percentage of the profit, citing some narrations from the Companions and their successors as evidence.