This is not “one or the another” situation, communism is the next qualitative stage in development of society. It solves the primary contradiction that we experience in capitalism, that is socialized production being privatized by individuals, aka capitalists.
You can’t just declare communism by signing a document, because it is a process of development in which small quantitative changes in production (socialism) lead to a qualitative change (communism), thus to achieve the communism stage you have to achieve a certain level of development.
This is why China is considered a communist country by marxists-leninist even though qualitatively it is a capitalist country. They are actively working to develop communism, this can be clearly seen throughout their rhetoric (i.e. “The Governance of China”) and their material results.