var counter = 2;
var limit = 5;
function addInput(divName){
     if (counter == limit)  {
          alert("You have reached the limit of adding " + counter + " pdb files");
     }
     else {
          var newdiv = document.createElement('div');
          newdiv.innerHTML = "Pdb File " + (counter + 1) + " <input type='file' name='pdbfiles[]'>";
          document.getElementById(divName).appendChild(newdiv);
          counter++;
     }
}