server.js

const express = require('express');    //Express Web Server
const path = require('path');     //used for file path
const fs = require('fs-extra');       //File System - for file manipulation
var uuid = require('node-uuid');
var exec = require('child_process').exec;
var Busboy = require('busboy');
const PORT = process.env.port || 9021;

var app = express();

app.get('/', function (req, res) {
  let home = __dirname+"/home.html";
  let stat = fs.statSync(home);
  var readStream = fs.createReadStream(home);
  var html = "";
  readStream.on('data', function (chunk) {
        html += chunk.toString().replace("@PORT", PORT);
  });
  readStream.on('end', function(){
    res.status(200).send(html);
  });

});


/* ==========================================================
Create a Route (/watermark) to handle the upload
(handle POST requests to /upload)
Express v4  Route definition
============================================================ */
app.route('/watermark')
    .post(function (req, res, next) {
        var busboy = new Busboy({ headers: req.headers });
        var fstream;
        var watermark,pdftowatermark='';

        let tempdir = '/tmp/' + uuid.v4()
        fs.mkdir(tempdir);
        let filesUploaded = 0;
        busboy.on('file', function (fieldname, file, filename, encoding, mimetype) {

            let localpath = tempdir+"/"+fieldname+'.pdf';
            fstream = fs.createWriteStream(localpath);
            file.pipe(fstream);

            fstream.on('close', function () {
                filesUploaded++;
                console.log('Uploaded File: ' + filename);

                if(fieldname == "pdf-to-watermark"){
                  pdftowatermark = localpath;
                }

                if(fieldname == "watermark"){
                  watermark = localpath;
                }

                if(filesUploaded == 2 && (watermark === undefined || pdftowatermark === undefined)){
                  res.status(500);
                  res.send("Two files uploaded but the file upload fields did not have the right names, did you name the fields watermark and pdf-to-watermark?\n");
                  return;
                }

                if(watermark && pdftowatermark){
                  let output_pdf = tempdir+'/output.pdf';

                  let cmd = "pdftk "+pdftowatermark+" multistamp "+watermark+" output "+output_pdf;
                  console.log('Running Command: ' + filename);
                  res.setHeader('Cmd', cmd);

                  exec(cmd, function (error, stdout, stderr) {
                    if(error){
                      console.error("Error Processing: "+output_pdf);
                      res.status(500);
                      res.send('Could not convert PDF');
                    } else {

                      let stat = fs.statSync(output_pdf);
                      console.error("File Saved and Streaming: "+output_pdf);
                      res.writeHead(200, {
                          'Content-Type': 'application/pdf',
                          'Content-Length': stat.size
                      });

                      var readStream = fs.createReadStream(output_pdf);
                      readStream.pipe(res);

                      exec('rm -rf ' + tempdir, function (err, stdout, stderr) {
                        if(err){
                          console.error("Could not delete "+tempdir);
                        } else {
                          console.log("Deleted "+tempdir);
                        }
                      });
                    }
                  });
                }
            });
        });
        req.pipe(busboy);
    });

app.listen(PORT);
console.log('Running on http://localhost:' + PORT);