To enable comments on future Pages/Posts, check “Allow people to post comments on new articles” in Settings -> Discussion. Then edit each published Page or Post and check “Allow comments” in each case. If you do not see this pane, click Screen Options at the very top of the page and check “Discussion”.
I might be missing something, but I am having the same problem and cannot get rid of the comments at the bottom of each page. I unchecked “Allow people to post comments on new articles” in Settings -> Discussion which I suppose should already clear all the pages from bottom comments. I also unchecked “Allow comments” from individual page settings – no result, the comments are still appear.