Javascript - Insert Data in to rendered PDF

How can we insert data(String,Integer,Image) into a PDF file. Here is the flow.

1) Load a PDF document from the local computer into a web page.

2) I should be able to drag and drop HTML elements on to the loaded PDF.

3) Then save the PDF.

I was going through this post, it seems a quite overwhelming. i'm not sure what approach to follow, dose conversion of PDF to HTML or Doc is possible, or we can insert directly into PDF.

Looking forwad for much needed help.

Thank you