gdocs-mailmerge.js

// Example usage, attach a similar trigger to your Spreadsheet's onFormSubmit event
function onFormSubmit(e) {
    var templateId = 'YOUR-DOCUMENT-ID-HERE',
        filenameTemplate = 'MailMerged Documents/<<Date>>/<<Client Name>>',
        documentId = mailMerge(templateId, filenameTemplate, e.namedValues);

    if (e.namedValues['Email PDF'])
        emailPdf(e.namedValues['Username'], documentId);
}

// Meat & Potatoes
function mailMerge(templateId, filenameTemplate, values) {
    var id = DocsList.getFileById(templateId).makeCopy('New MailMerge ' + Math.random().toString(36).substr(2, 12)).getId(),
        doc = DocumentApp.openById(id),
        pathSplitIndex = filenameTemplate.lastIndexOf('/'),
        path = null, filename = filenameTemplate;
    
    if (pathSplitIndex > 0) {
        path = filenameTemplate.substr(0, pathSplitIndex);
        filename = filenameTemplate.substr(pathSplitIndex + 1);
    }
  
    for (var key in values) {
        var value = values[key][0];
        key = '<<' + key + '>>';
        path = path.replace(key, value);
        filename = filename.replace(key, value);
        doc.replaceText(key, value);
    }
    doc.setName(filename).saveAndClose();
    if (path) {
        var pathId = DocsList.getFolder(path);
        DocsList.getFileById(id).addToFolder(pathId);
    }

    return doc.getId();
}

function emailPdf(email, docId, body) {
    var doc = DocumentApp.openById(docId),
        pdf = doc.getAs('application/pdf'),
        subject = doc.getName();
    if (body === undefined)
        body = 'PDF Attached: ' + doc.getName();

    MailApp.sendEmail(email, subject, body, {htmlBody: body, attachments: pdf});
}