Is it permissible to demand and take money from a contractor who exploited an engineer's certificate without her knowledge for more than two years after the expiration of the agreed-upon contract, knowing that she did not perform any actual work for him other than lending him her certificate for tender requirements?

This contract is impermissible due to its inclusion of deception and fraud, as the state requires the presence of an engineer to supervise the works and ensure quality, and you did not supervise any project. Therefore, the money earned from this contract must be disposed of by spending it on charitable causes and public welfare, and it should not be returned to the contractor. Furthermore, you are not permitted to demand money from the institution for their future exploitation of your certificate; rather, the matter must be rectified by informing the responsible authorities to stop this deception.