Is copying an original Windows disc from the company without its owner's knowledge considered forbidden, especially if doing so saves a large amount of money, and does it fall under the category of betraying the employer or the manufacturing company?

An employee is not permitted to dispose of his employer's property except in matters for which he has been granted permission; otherwise, he would be betraying a trust, as Allah Almighty says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know." Therefore, if the questioner's friend duplicated the CD without permission, he has committed a sin and must seek absolution from the company owner and repent to Allah. However, if he was granted permission, then it must be considered whether the manufacturer of the CD permitted its duplication. If they did not permit it, then it is not permissible to duplicate it, even if the employer gave permission, because that would be an infringement upon the rights of others.