Download and open PDF file using Ajax

Here is how I got this working

$.ajax({
  url: '<URL_TO_FILE>',
  success: function(data) {
    var blob=new Blob([data]);
    var link=document.createElement('a');
    link.href=window.URL.createObjectURL(blob);
    link.download="<FILENAME_TO_SAVE_WITH_EXTENSION>";
    link.click();
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

Updated answer using download.js

$.ajax({
  url: '<URL_TO_FILE>',
  success: download.bind(true, "<FILENAME_TO_SAVE_WITH_EXTENSION>", "<FILE_MIME_TYPE>")
});

You don't necessarily need Ajax for this. Just an <a> link is enough if you set the content-disposition to attachment in the server side code. This way the parent page will just stay open, if that was your major concern (why would you unnecessarily have chosen Ajax for this otherwise?). Besides, there is no way to handle this nicely acynchronously. PDF is not character data. It's binary data. You can't do stuff like $(element).load(). You want to use completely new request for this. For that <a href="pdfservlet/filename.pdf">pdf</a> is perfectly suitable.

To assist you more with the server side code, you'll need to tell more about the language used and post an excerpt of the code attempts.

I don't really think that any of the past answers spotted out the problem of the original poster. They all presume a GET request while the poster was trying to POST data and get a download in response.

In the course of searching for any better answer we found this jQuery Plugin for Requesting Ajax-like File Downloads.

In its "heart" it creates a "temporary" HTML form containing the given data as input fields. This form is appended to the document and posted to the desired URL. Right after that the form is removed again:

jQuery('<form action="'+ url +'" method="'+ (method||'post') +'">'+inputs+'</form>')
    .appendTo('body').submit().remove()

Update Mayur's answer looks pretty promising and very simple in comparison to the jQuery plug-in I referred to.

This is how i solve this issue.
The answer of Jonathan Amend on this post helped me a lot.
The example below is simplified.

For more details, the above source code is able to download a file using a JQuery Ajax request (GET, POST, PUT etc). It, also, helps to upload parameters as JSON and to change the content type to application/json (my default).

The html source:

<form method="POST">
    <input type="text" name="startDate"/>
    <input type="text" name="endDate"/>
    <input type="text" name="startDate"/>
    <select name="reportTimeDetail">
        <option value="1">1</option>
    </select>
    <button type="submit"> Submit</button>
</form>  

A simple form with two input text, one select and a button element.

The javascript page source:

<script type="text/javascript" src="JQuery 1.11.0 link"></script>
<script type="text/javascript">
    // File Download on form submition.
    $(document).on("ready", function(){
        $("form button").on("click", function (event) {
            event.stopPropagation(); // Do not propagate the event.

            // Create an object that will manage to download the file.
            new AjaxDownloadFile({
                url: "url that returns a file",
                data: JSON.stringify($("form").serializeObject())
            });

            return false; // Do not submit the form.
        });
    });
</script>  

A simple event on button click. It creates an AjaxDownloadFile object. The AjaxDownloadFile class source is below.

The AjaxDownloadFile class source:

var AjaxDownloadFile = function (configurationSettings) {
    // Standard settings.
    this.settings = {
        // JQuery AJAX default attributes.
        url: "",
        type: "POST",
        headers: {
            "Content-Type": "application/json; charset=UTF-8"
        },
        data: {},
        // Custom events.
        onSuccessStart: function (response, status, xhr, self) {
        },
        onSuccessFinish: function (response, status, xhr, self, filename) {
        },
        onErrorOccured: function (response, status, xhr, self) {
        }
    };
    this.download = function () {
        var self = this;
        $.ajax({
            type: this.settings.type,
            url: this.settings.url,
            headers: this.settings.headers,
            data: this.settings.data,
            success: function (response, status, xhr) {
                // Start custom event.
                self.settings.onSuccessStart(response, status, xhr, self);

                // Check if a filename is existing on the response headers.
                var filename = "";
                var disposition = xhr.getResponseHeader("Content-Disposition");
                if (disposition && disposition.indexOf("attachment") !== -1) {
                    var filenameRegex = /filename[^;=\n]*=(([""]).*?\2|[^;\n]*)/;
                    var matches = filenameRegex.exec(disposition);
                    if (matches != null && matches[1])
                        filename = matches[1].replace(/[""]/g, "");
                }

                var type = xhr.getResponseHeader("Content-Type");
                var blob = new Blob([response], {type: type});

                if (typeof window.navigator.msSaveBlob !== "undefined") {
                    // IE workaround for "HTML7007: One or more blob URLs were revoked by closing the blob for which they were created. These URLs will no longer resolve as the data backing the URL has been freed.
                    window.navigator.msSaveBlob(blob, filename);
                } else {
                    var URL = window.URL || window.webkitURL;
                    var downloadUrl = URL.createObjectURL(blob);

                    if (filename) {
                        // Use HTML5 a[download] attribute to specify filename.
                        var a = document.createElement("a");
                        // Safari doesn"t support this yet.
                        if (typeof a.download === "undefined") {
                            window.location = downloadUrl;
                        } else {
                            a.href = downloadUrl;
                            a.download = filename;
                            document.body.appendChild(a);
                            a.click();
                        }
                    } else {
                        window.location = downloadUrl;
                    }

                    setTimeout(function () {
                        URL.revokeObjectURL(downloadUrl);
                    }, 100); // Cleanup
                }

                // Final custom event.
                self.settings.onSuccessFinish(response, status, xhr, self, filename);
            },
            error: function (response, status, xhr) {
                // Custom event to handle the error.
                self.settings.onErrorOccured(response, status, xhr, self);
            }
        });
    };
    // Constructor.
    {
        // Merge settings.
        $.extend(this.settings, configurationSettings);
        // Make the request.
        this.download();
    }
};

I created this class to added to my JS library. It is reusable. Hope that helps.