How do I cite the Universal Declaration of Human Rights using APA referencing style?

The Universal Declaration of Human Rights can be cited as a 'document found online' if using the webpage: https://www.un.org/en/about-us/universal-declaration-of-human-rights or the pdf: https://www.un.org/sites/un2.un.org/files/2021/03/udhr.pdf 

The UDHR is not classed as a treaty or a legally binding document (although it influences the development of legally binding treaties internationally), so should not be cited as such.

The elements to note for in-text and reference list formats for online documents are:

Author: UN General Assembly
Publication date: 1948
Title: Universal declaration of human rights

Document number in brackets [optional]: (217 (III) A)
Location: URL or pdf hyperlink (depending on the document format you have viewed)

For more, see the official APA Style website's Report by a Government Agency References page linked below for an example of how a citation with a document number should be formatted.