title: Free PDF API in PHP to annotate
body: <p>Can any one suggest me the <strong>Free PDF API</strong> in PHP to meet the following requirement.I am working on one web app. so it requires the following features. 
  1) allow the PDF reader to annotate on the selected text. 
  2) reply to the annotation.
  3) able to remove added annotations.</p>
  
  <p>is it possible to add annotation through Javascript?</p>