How to prevent the page from opening outside of an iframe?

Unfortunately there will always be ways to circumvent this type of block mainly with the use of javascript, but for the laymen, simple validation would suffice.

function IsFrame () {
    try {
        return window.self !== window.top;
    } catch (e) {
        return true;
    }
}

Use the code below to verify that the window in which the page was loaded is the browser window itself, not an iframe:

if(window==window.top) {
    // Página não está em iframe, portanto lança um erro.
    throw new Error('Esta página somente pode ser carregada em um iframe!');
}