var CONST = {
    author_license: [some user id],
    replyTo: 'set this or pull it from somewhere',
    bcc: 'whatever you wish'
}

function sendEmail_WF() {

    var po = nlapiGetNewRecord();

    var emailMerger = nlapiCreateEmailMerger(yourFormId);
    emailMerger.setTransaction(po.getId());
    emailMerger.setEntity('vendor', po.getFieldValue('entity'));
    var mergeResult = emailMerger.merge();
    var subject = mergeResult.getSubject();
    var body = mergeResult.getBody();

    var recipient = getReceipients(po.getFieldValue('entity'));
    if (recipient.length == 0) {
        throw 'There is no email address to send this email to.';
    }

    var attachments = [];
    attachments = getAttachment(attachments, po);
    attachments = getPDF(attachments, po);

    var records = {
        transaction: po.getId()
    }

    if (recipient && recipient != '') {
        nlapiSendEmail(CONST.author_license, recipient, subject, body, null, CONST.bcc, records, attachments, null, null, CONST.replyTo);
    }
}

function getReceipients(vendId) {
    // Here we pull email addresses from the vendor's contacts and also addd the vendor's main email address

    var recipient = [];
    recipient.push(nlapiLookupField('entity', vendId, 'email'));
    var cS = nlapiSearchRecord("contact", null,
        [
            ["company", "anyof", vendId],
            "AND",
            ["custentity_is_po_recipient", "is", "T"],
            "AND",
            ["email", "isnotempty", ""]
        ]
    );
    for (var i = 0; cS && i < cS.length; i++) {
        recipient.push(cS[i].getId());
    }

    var recipientNoDupe = [];
    recipient.forEach(function (recipient) {
        if (recipientNoDupe.indexOf(recipient) < 0) {
            recipientNoDupe.push(recipient);
        }
    });

    return recipientNoDupe;

}

function getAttachment(attachments, po) {
    varcustbody_your_document_field = po.getFieldValue('custbody_your_document_field');
    if (custbody_your_document_field && custbody_your_document_field != '') {
        attachments.push(nlapiLoadFile(custbody_your_document_field));
    }
    return attachments;
}

function getPDF(attachments, po) {
    var paras = [];
    paras.formnumber = 'your transaction form id';
    var file = nlapiPrintRecord('TRANSACTION', po.getId(), 'PDF', paras);
    attachments.push(file);
    return attachments;
}​