Joseph Conrad's novel Heart of Darkness can be considered a Post-colonial text if one examines the exploitation depicted in the novel.
When Marlow is speaking about his position as a steamer pilot, he details what he came upon at the company's Lower Station. The native inhabitants are described as being salves to the Belgium company's hired guards. The Africans are starving to death and not being treated well. Instead, they are forced to work to physical exhaustion.
Therefore, the novella depicts how native inhabitants are treated when other countries come in to colonize. These inhabitants are exploited and forced into servitude. Given that Post-colonial literature is meant to speak against colonization, the treatment of the natives shows both Marlow's and Conrad's views on what happens when some locations are colonized (when the colonization is not beneficial to all).
Though Heart of Darkness was written during the colonial period, it has some elements of post-colonial literature. For example, it presents the darker side of colonialism in Africa, not just the standard European narrative of white people bringing prosperity and progress to the Congo. Instead, Europeans, personified in the figure of Kurtz, bring degradation, death, and destruction to the Congo. Also, the novella presents characters who are in direct opposition to the stereotypes in colonial discourse. While colonial discourse characterized Africans as untamed or evil, this novel instead presents the Europeans as bloodthirsty and evil. The stereotypes that Europeans unfairly associated with Africans are instead turned around and applied to Europeans in this work.
In addition, post-colonial narratives often have multiple narrative strands, emphasizing that there is more than one way to tell the story of colonialism. In Heart of Darkness, Marlow's tale is framed by the tale of the unnamed narrator who is on the ship in England listening to Marlow. In addition, Marlow presents Kurtz's story within his own narrative, leading to the kinds of multiple perspectives that are common in post-colonial literature.