PDF Expert 7 lets you easily create folders and subfolders as well as move files and folders to organize them in the best possible way.
In the same way, you can add a new folder inside an existing one.
Just tap and hold on a file or folder and drag it to the destination folder.
When you drag one file over the other, PDF Expert offers you an option to create a folder containing these files.
Here's an alternative way to move files or folders: