Is it permissible to buy gifts to be placed in a company where non-Muslims work, as an expression of Christmas and a way of participating with them?

It is not permissible to participate in birthday celebrations by offering gifts, suspending work, or putting up decorations, nor is it permissible to offer congratulations for them. This is because they are an innovation (bid'ah), prohibited, and associated with corrupt beliefs. Celebrating them involves imitating Christians, and the Prophet, peace and blessings be upon him, said: "Whoever imitates a people is one of them."