Stamp on certain location of pdf using iText

I was trying to get the location using javascript and passed the coordinates to apply stamp on the stamp but it does not work properly. Below is the function I used to capture the coordinates of the mouse pointer.

function divMove(e){
  var div = document.getElementById('stamp');
  div.style.position = 'absolute';
  //div.style.top = e.clientY + 'px';
  //div.style.left = e.clientX + 'px';
  var box = div.getBoundingClientRect();
  mouse_top = e.clientY;
  mouse_left = e.clientX;
  var diff_x = mouse_left - box.left;
  var diff_y = mouse_top - box.top;
  div.style.top = ((Number(div.style.top.replace("px", "")) - 1) + diff_y) +"px";
  div.style.left = ((Number(div.style.left.replace("px", "")) - 1) + diff_x) +"px";
  document.getElementById("data").innerHTML =
    "mouse_top:" + mouse_top + "<br>mouse_left:" + mouse_left
}

Below is the back-end code to handle the stamping part using iText:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  Properties p = new Properties();
  p.load(new FileInputStream("config.properties"));

  String src = p.getProperty("src");
  String dest = p.getProperty("dest");
  String imgSrc = p.getProperty("stamp");

  PdfDocument doc = new PdfDocument(new PdfReader(src), new PdfWriter(dest));

  ImageData image = ImageDataFactory.create(imgSrc);
  float w = image.getWidth();
  float h = image.getHeight();
  System.out.println("w: " + w + ", h: " + h);

  float mouseX = Float.valueOf(request.getParameter("mouseTop"));
  float mouseY = Float.valueOf(request.getParameter("mouseLeft"));
  System.out.println("top: " + mouseX + ", left: " + mouseY);

  //Rectangle rect = new Rectangle(Math.abs(mouseX-600)+w,Math.abs(mouseY-300)+h,w,h);
  Rectangle rect = new Rectangle(mouseX,mouseY,w,h);
  PdfStampAnnotation stamp = new PdfStampAnnotation(rect).setStampName(new PdfName("Approved"));
  PdfFormXObject xObj = new PdfFormXObject(new Rectangle(w,h));
  PdfCanvas canvas = new PdfCanvas(xObj,doc);
  canvas.addImage(image,0,0,false);
  //canvas.getGraphicsState();

  stamp.setNormalAppearance(xObj.getPdfObject());
  stamp.setFlags(PdfAnnotation.PRINT);
  stamp.setFlags(PdfAnnotation.LOCKED);

  for(int i=1;i<=doc.getNumberOfPages();i++) {
    doc.getPage(i).addAnnotation(stamp);
  }
  //doc.getFirstPage().addAnnotation(stamp);
  FileOutputStream out = new FileOutputStream("config.properties");
  p.setProperty("src", dest);
  p.setProperty("dest", src);
  p.store(out, null);
  out.close();
  doc.close();

  //first read the file to byte array
  try {
    File file = new File(dest);

    if(file.canRead()) {
      String base64File;

      //define the byte array to store the file
      byte[] byteFile = new byte[(int)file.length()];

      //define the stream to read the pdf
      ByteArrayOutputStream bytes = new ByteArrayOutputStream();
      FileInputStream fis = new FileInputStream(file);

      //convert the read file's stream byte to base64
      //important for streaming the pdf bytes back to the front
      Base64OutputStream baos = new Base64OutputStream(bytes);

      int len;

      //read the byte from file then write it through stream to byteFile variable
      //read is reading one by one
      while((len = fis.read(byteFile)) > 0){
        baos.write(byteFile,0,len);
      }
      baos.flush();

      // turn the read byte into string
      base64File = bytes.toString("UTF-8");

      bytes.close();
      baos.close();
      fis.close();

      response.setContentType("application/pdf");
      response.setHeader("Content-Disposition","inline");
      response.setCharacterEncoding("UTF-8");
      response.setContentLength(base64File.length());
      //write the base64 string to the response message body
      response.getWriter().write(base64File,0,base64File.length());
              //response.getOutputStream().write(base64File,0,base64File.length());

    } else {
      response.setCharacterEncoding("UTF-8");
      response.getWriter().write("File is unreadable!");
    }

  } catch(FileNotFoundException e) {
    e.printStackTrace();
  } catch(Exception e) {
    e.printStackTrace();
  }
}

This is the position I am going to stamp:

The output is not what I expected:

from Stamp on certain location of pdf using iText