Tinymist in VS Code does this out of the box (and looks like it can be set up in other editors). That or you can configure it to save out a new PDF automaticall

Tinymist in VS Code does this out of the box (and looks like it can be set up in other editors). That or you can configure it to save out a new PDF automatically on save or as you edit the document and just open it in a PDF viewer that'll reload when the file changes.