Conrad's masterpiece takes special cases of morality as one of its central themes. The company is symbolic of a special case of morality, meaning it is an entity that defines a set of moral rules for itself to follow which are decidedly specific and far from universal.
To justify its actions in Africa the company claims that the shareholders are ultimately responsible for the pillaging and death that take place in the course of doing business. The men in Africa doing the work of shipping the ivory are mandated to take whatever measures are necessary to procure the ivory the company needs because the shareholders demand results.
Essentially, the men doing the work of the company are given a set of moral rules that will allow them to forgo the morality of Europe and "civilization".
Kurtz understands this moral departure to be his mandate and goes further.
It is through the work (or what passes for it) that Kurtz does in Africa that his moral bankruptcy is revealed.
He creates, or attempts to create, a moral world of his own with rules and laws of right and wrong of his own making. Taking the moral allowance offered to him to complete his task in the jungle, Kurtz not only rejects the morality of Europe but attempts to replace it.