iOS – Taking a Screenshot on iPhone X

Orientation lock on iPhone with iOS 4 only does portrait lock at the moment. Hopefully they will have landscape lock on the next update.

Webshot Free can do this (there's a 99¢ ad-free version too). It's supposed to let you just change http:// to webshot:// and it will open the same URL in in the app. That didn't work, but cut+paste did.

There may be other apps which are better for certain needs, depending on what you want to actually do with the page. If you just want a JPG or PNG of it, Webshot Free works fine.

If you are trying to save a page for reading later, iCab Mobile ($2, universal) will let you save a .webarchive or a .pdf file. [Note: the print to pdf function is actually provided by 3rd party webapps, but it's integrated into iCab].

There are a variety of "Print to PDF" apps in the app store, PrintBureau, seems to be one of the better ones (and is universal).