You missunderstood the intent of the sentence. ...

You can copy a GIF, but you couldn't edit the words in it, so you must copy the text of the HTML document on FOLDOC, edit the words, and submit your modified copy to me.

I presented the example as a GIF because, had I left it as in HTML, you could "cheat" by coping my example - I wouldn't be able to detect that. So I presented the text as a picture (a GIF file). The difference is copying a GIF and copying text in HTML.