This article explains the situations when you can use the full screen on the iPad and how to do it.

Putting Safari in full screen is appealing if you want the most immersive web browsing experience. While there’s no full screen button in Safari, there are a few ways to use more of your tablet’s screen. Here are your options:

Tap the aA button to the left of the page URL, then tap Hide Toolbar. The page won't go completely full screen, but it's the closest you'll get.

Tap the menu button at the top left of Safari. This will collapse the menu and give you much more room to view web pages.