It will depend upon the article source content, how the conversion styling is preserved when converted to RTF format on the clipboard, and how Pages reconciles that clipboard formatting when pasting. If copying web page content, know that various web browsers may paste content differently on the clipboard and that can potentially corrupt how Pages handles pasted content.
Pages offers two different paste entries on its Edit menu. If neither provides satisfying results, then you may need to first paste into another application (e.g.TextEdit). Once done, you select and copy that intermediate result to the clipboard and paste it into Pages. The last sentence in the first paragraph may mean you start with Safari instead of other third-party browsers.