Ajax Download PDF output PDF is Blank

Question

I am trying Ajax download PDF. Following is my Ajax code:

$.ajax({
    // `url` 
    url: "/pdf/download",
    type: "GET",
    contentType: "application/octet-stream; charset=utf-8",
    // `custom header`
    headers: {
        "OAuth-Token": api.getOAuthToken()
    },
    beforeSend: function (jqxhr) {
        console.log(this.headers);
        alert("custom headers" + JSON.stringify(this.headers));
    },
    success: function (data) {
        // `file download`
        $("a")
            .attr({
            "href": data.file,
                "download": "file.pdf"
        })
            .html($("a").attr("download"))
            .get(0).click();
        //console.log(JSON.parse(JSON.stringify(data)));
    },
    error: function (jqxhr, textStatus, errorThrown) {
      console.log(textStatus, errorThrown)
    }
});

Following is my PHP Header Script:

$api->setHeader('Content-Transfer-Encoding', 'binary');
$api->setHeader('Cache-Control', 'public, must-revalidate, max-age=0');
$api->setHeader('Pragma', 'public');
$api->setHeader('Expires', 'Sat, 26 Jul 1997 05:00:00 GMT');
$api->setHeader('Last-Modified', $now->format(TimeDate::RFC2616_FORMAT));
$api->setHeader('Content-Type', 'application/pdf');
$api->setHeader(
    'Content-Disposition',
    'attachment; filename="' . getPdfName() . '.pdf"'
);

The above Ajac call with OAuth-Tocken is working fine but i receive the output like the following and the PDF is Blank and cannout open sometimes.

%PDF-1.4 %âãÏÓ 3 0 obj <

The above return data is justa sample of return data. Can some one tell me how can create a valide PDF from the data?

NOTE: I am trying to do this method because i couldnt able to achive sugarcrm fileDownload error after upgrade download in SugarCRM after latest update.