Is it permissible to receive compensation for sick leave days from the Social Security Fund, in addition to full pay from the company, knowing that these days were actually worked?

The answer covers two points: the ruling on participating in the social security fund and the conditions for eligibility for the money. If the fund's conditions prevent the employee from taking the amount, then it is not permissible for him to take it, and he must return it. If the conditions allow him to do so, then there is no objection, based on the hadith: "Muslims are bound by their conditions."