I think you're confusing text documents like PDF or word .doc(x) type files for "plain text". Plain text doesn't contain hidden anything at all. It's just plain text and nothing else. That's why a plain text editor is completely different from Microsoft Word, or OpenOffice. They both edit textual document types, but a plain text editor doesn't do metadata, fancy fonts, colors, styles, or any of the fun junk you find in PDF and other textual document types. It does only text.