Is buying shares in a company after learning about its profits through one's job as an auditor considered an exploitation of the position?

There is no Shar'i (Islamic legal) impediment to purchasing these shares, unless you exploit your knowledge of them by spreading rumors that they are unprofitable, so that people refrain from buying them and you can acquire them exclusively. In such a case, this action would be forbidden from two perspectives: your reporting of information contrary to reality, which is pure falsehood, and your betrayal of the company for which you are an employee.