create link to download file I'm adapting a drupal module to my need. It permit to upload a pdf to insert it into a node add form in an iframe to display the file.
I've need also to insert a link to download the previous uploaded file.

I've read and try thousand of guide and documentation but nothing that work or adapt to my scope.

Is possible to find an easy way to create by code a download link?
It sounds like you're looking for the PDF Reader module. 


  PDF Reader will render your entity file fields with the selected PDF
  renderer.
  
  The implemented PDF renderers are:
  
  
  Google Docs Viewer 
  pdf.js - PDF Reader in JavaScript 
  Direct PDF embed
  Microsoft Office Web Viewer(7.x-2.x-dev)
  


This module lets you specify any file field to render as a PDF embedded in a node. It also has an option to display download link for the embedded PDF.