I could be wrong, but the latest version of Goodreader does NOT access cloud files other than its own. If there's a way to do what you describe PLEASE enlighten us!!
re: Can Goodreader access files & folders that aren't in the Goodreader folder?
From what I can tell, it will allow you to choose a specific folder when you select "export to iCloud Drive", however, it will not allow you to access that non-Goodreader folder to view the file even though you can readily see it in the folder it was exported to when you login to iCloud Drive via a computer.