jQuery has some issues loading binary data using AJAX requests, as it does not yet implement some HTML5 XHR v2 capabilities, see this enhancement request and this discussion
Given that, you have one of two solutions:
First solution, abandon JQuery and use XMLHTTPRequest
Go with the native HTMLHTTPRequest, here is the code to do what you need
var req = new XMLHttpRequest();
req.open("GET", "/file.pdf", true);
req.responseType = "blob";
req.onload = function (event) {
var blob = req.response;
console.log(blob.size);
var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download="Dossier_" + new Date() + ".pdf";
link.click();
};
req.send();
Second solution, use the jquery-ajax-native plugin
The plugin can be found here and can be used to the XHR V2 capabilities missing in JQuery, here is a sample code how to use it
$.ajax({
dataType: 'native',
url: "/file.pdf",
xhrFields: {
responseType: 'blob'
},
success: function(blob){
console.log(blob.size);
var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download="Dossier_" + new Date() + ".pdf";
link.click();
}
});