webpage vs text file

webpage and text file both are nouns.

Word	Noun	Adjective	Verb	Adverb
webpage	Yes	No	No	No
text file	Yes	No	No	No

As nouns, text file is a hypernym of webpage; that is, text file is a word with a broader meaning than webpage:

webpage: a document connected to the World Wide Web and viewable by anyone connected to the internet who has a web browser
text file: (computer science) a computer file that contains text (and possibly formatting instructions) using seven-bit ASCII characters

Other hypernyms of webpage include document.

webpage (noun)	text file (noun)
a document connected to the World Wide Web and viewable by anyone connected to the internet who has a web browser	(computer science) a computer file that contains text (and possibly formatting instructions) using seven-bit ASCII characters