EntMetaData.set(key, value);

try {
  var doc = app.documents.item(0);

  // Access the document’s metadata
  var md = doc.entMetaData;

  // Iterate the metadata keys and values
  for (var i = 0; i < md.length; ++i) {
    var keyValue = md.item(i);
    $.writeln("Key: [" + keyValue[0] + "], Value: [" + keyValue[1] + "]");
  }

  // Access the value of a specific key
  var mdName = md.get("Core_Name");
  $.writeln("Name: [" + mdName + "]");

  md.set("C_CUSTOM_BOOLEAN", "true");

  var mdID = md.item("Core_ID");
  $.writeln("ID: [" + mdID + "]");
} catch (e) {
  desc = e.description;
  num = e.number;
  alert("error " + num + ": " + desc);
}