window.opener in mvc 3

You could use a normal link with target="_blank" attribute:

@Html.ActionLink(
    "Generate PDF",
    "GeneratePdf",
    "MyController",
    null,
    new {
        url = "some url",
        target = "_blank"
    }
)

or if you want a button you could use javascript in separate JS file you can use Jquery:

$(function() {
    $('#btnID').click(function() {
        // get the url of the data-pdf-url property of the button
        var url = $(this).data('data');
        window.open(url, 'data');
        return false;
    });
});