错误：未在Google文档

Question

我经常收到此错误“未定义DocumentApp”。我正在使用驱动器api与谷歌驱动器。当我尝试使用

获取当前打开的Google文档时

DocumentApp.openById('My-file-Id');

但我不断收到此错误“ documentApp未定义”。请帮我解决或者告诉我正确的方法。

function printFile(fileId) 
{
    $("#demo_scope").collapse('show');

    var response_data = '<span class="custome_span_text"><center><img src="<?php echo base_url("img/loading.gif");?> "> Wait open the document ...</center></span>';

    $("#google_drive_iframe").show();
    $("#google_drive_iframe").html(response_data);

    var request = gapi.client.drive.files.get({
       'fileId': fileId
    });

    request.execute(function(resp) 
    {
        if(resp.code != 404)
        {
            file = resp;
            var file_id = file.id;

            var some_magic = DocumentApp.openById('My-file-Id');    <!-- Here i am getting error -->

            var file_title = file.title; 
            var file_modifiedDate =  new Date(file.modifiedDate);
            var exportLinks = file.exportLinks;
            var exportLink_html = exportLinks["text/html"];
            $("#google_doc_filenm").val(file_title);
            $("#doc_file_id").val(file_id);
            $("#google_drive_iframe").show(); 
            $("#google_drive_iframe").html('<iframe  src="'+file.alternateLink+'" onclick="checkFocus();"  class="google_iframe"></iframe>');
        }
        else
        {
            $("#google_drive_iframe").html("<center><span class='error_title'><i class='glyphicon glyphicon-remove'></i> Google Document has been not available !</span></center>");
            alertify.error("Please select google document");
            return false;
        }
    });
}