Send mail with attachment (PDF) using Gmail API

Problem

All the data is sent in text format rather than as PDF as an attachment.

My Code

var boundary = "__myapp__", nl = "\n";
// var attach = data.toString("base64");
var fileName = "abc.pdf";
var attach = new Buffer(fs.readFileSync("./" + fileName)).toString("base64");

var str = ["Content-Type: text/plain; charset=\"UTF-8\"\n",
    "MIME-Version: 1.0\n",
    "Content-Transfer-Encoding: 7bit\n",
    "to: ", to, "\n",
    "subject: ", subject, "\n\n",
    "Content-Type: multipart/alternate; boundary=" + boundary + nl,
    "--" + boundary,
    "Content-Type: text/plain; charset=UTF-8",
    "Content-Transfer-Encoding: 7bit" + nl,
    message + nl,
    "--" + boundary,
    "--" + boundary,
    "Content-Type: Application/pdf; name=myPdf.pdf",
    'Content-Disposition: attachment; filename=myPdf.pdf',
    "Content-Transfer-Encoding: base64" + nl,
    attach,
    "--" + boundary + "--"
].join('');

var encodedMail = new Buffer(str).toString("base64")
    .replace(/\+/g, '-')
    .replace(/\//g, '_');

resolve(encodedMail);

A part of mail is as below

Content-Type: multipart/alternate; boundary=myapp --_myapp_Content-Type: text/plain; charset=UTF-8Content-Transfer-Encoding: 7bit test message --myapp--_myapp_Content-Type: Application/pdf; name=myPdf.pdfContent-Disposition: attachment; filename=myPdf.pdfContent-Transfer-Encoding: base64 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...more texts...at last...==--myapp--

What I think is that there might be some issue with the template of sending the mail with attachment.

Can anyone provide help here?
Thanks