Highlighting a Downloaded Website?

I have a small downloaded website in DTP on music arranging. I would like to highlight different areas on different pages.

When I select the ‘main/front page’ in DTP, it is shown in the regular preview panel below, and I’m also able to open the editing bar and choose to highlight anything I want to.

If I then click on a link of that front page, I get taken to that linked page (as it’s one of the ones captured when I downloaded the website). However, the editing tools, and also trying to choose Format > Highlight, are greyed out, and I cannot highlight anything.

So the front page is OK to highlight, but not any of the further downloaded pages.

Couple of observations - both pages are labelled as kind ‘HTML document’. I also thought maybe it was loading in the linked page from the web rather than my captured files, so I disconnected the internet and tried - same result.

When I go directly to the linked page by choosing it from my own list of downloaded files, then, I can highlight material. So I’m just really confused as to what is going on here.

Any help gratefully accepted.

You have to directly open the downloaded page you want to modify.