If you want to Hide "SentTo" menu from document library then this can be done by many ways, but I am going to explain simplest one. we can do this by modifying core.js, but it can be harmful for your site because it is very important file.

Here I am not going to modifying Core.js ,So in order to hide menu we have to perform following steps :

  1. Go to document library
  2. Now edit this page and add a content editor web part
  3. Now open it's HTML source
  4. Insert following script

    <script>

    AddSendSubMenu = function (m, ctx) { }
    _spBodyOnLoadFunctionNames.push("resetAddSendSubMenu()");

    function resetAddSendSubMenu() {

    AddSendSubMenu = function (m, ctx) { };

    }

    </script>


  5. Save and close

This can be done on your desired pages manally but if you want to hide SentTo menu from all pages then you have to insert this code to your master page.