Thanks to Joachim, I found a solution that fit exactly to my needs. I use javascript to open a new window with the document in it.
Here is the javascript:
function openPDF(source, name) {
var screenHeight = screen.height;
var height = screenHeight - 100;
var width = height / (1.3);
var specs = 'directories=0, location=0, toolbar=0, menubar=0, resizable=1, status=0';
specs += ', height=' + height;
specs += ', width=' + width;
specs += ', left=' + (screen.width - width)/2;
specs += ', top=' + 10;
window.open(source, name, specs);
return false;
}
And the button:
<a href="#" target="_blank" wicket:id="list.openbutton"
class="button openbutton" onClick="return openPDF(this.href, 'PDF file')">Open</a>