Is it permissible for an engineer to sell the technical study in his possession to the contractor who is carrying out the works, given that the contractor is required to submit a similar executive study?

It is permissible to sell the executive study to the one who was awarded the contract if the employer grants permission; otherwise, it is not. This is because it negatively impacts the quality of work and the monitoring of its execution, and it may fall under the meaning of "ghulul" (embezzlement from public funds or booty), as indicated by the evidence.