The document isn't "using" anything, since a document is a passive object. Unless you have something like vim modelines where you configure it at the top of the file like `/* vim: set tabstop=8:softtabstop=8:shiftwidth=8:noexpandtab */ `, the document itself doesn't know anything about how things _should_ be (which is the important part).

an opened document inside an editor is absolutely aware of this, and this is what you're collaborating on. almost all IDEs support EditorConfig, which makes standardizing on things like that across teams trivial.