He is temporarily in charge of the company and is trying to feather his nest.

The idiom feather their own nest means to enrich oneself by using one's influence or position or with other people's money. The option that best captures this idea is option C.

Option A suggests improving the company's reputation, which is not related to personal gain.

Option B refers to managing the company, but it’s not about self-interest.

Option D means changing or expanding the company's offerings, which is not related to personal enrichment.