如何将文件从主包复制到文档文件夹

I want to check one file in Document folder.I want if this file not exist in document folder copy it from main bundle to document folder. I write this code and this file to be copy but my problem here.....!!!! my file is .sqlite file (Database file) and when copy to document folder hasn't data in self!!!! why??? while the this file when is in main bundle has data in self.I want to check one file in Document folder.I w