Retrieve Iist Item column values with column names on Item click, JavaScript

You can get column/fields name from list unless they are not consistent and then use them to fetch values for each key, here's how you can get all fields for a list,

function loadFieldCustProperty() {
        var clientContext = new SP.ClientContext();
        var targetList = clientContext.get_web().get_lists().getByTitle('List Title');
        fieldCollection = targetList.get_fields();
        clientContext.load(fieldCollection);
        clientContext.executeQueryAsync(onQuerySucceeded, onQueryFailed);


        function onQuerySucceeded() {

            var fe = fieldCollection.getEnumerator();
            while (fe.moveNext()) {
                var  field = fe.get_current();

                var xmlSchemaString = field.get_schemaXml();
                var fieldXml = parseXml(xmlSchemaString);
                var fieldElement = fieldXml.getElementsByTagName('Field')[0];
                var fieldPropertyValue = fieldElement.getAttribute('ColName'); //get ColName property value

                //...
            }

        }

        function onQueryFailed(sender, args) {
            //error handling goes here...
        }

    }

View custom field property value using JavaScript

Then, in here

currentItemGUID = pdfItem.get_item('UniqueId'); // here use field names e.g. using a enumerator for getting each column's value for selected item.

Also you might want to look at this question Javascript to get GUID from SharePoint