When a folder from Windows Explorer is imported into Ultra Recall, all of its subfolders and files can be imported (by default maintaining their original directory structure) with the Import Wizard by using the Folder option.
If files or folders are later added to the Windows folder or are modified either in Ultra Recall or externally, you can easily re-synchronize these new/updated files and folders by Synchronizing the folder using Item | Synchronize on the menu bar. If you only want to add any new external files and/or folders, simply re-import the same root folder to the same location in the Data Explorer Pane with the Create logically linked items for duplicate URLs checkbox is checked. You can either check this option on the Select Destination page of the Import Wizard each time you import, or you can configure this to be the global default at Tools | Options | Import (more).
You can also directly assign a URL attribute with a folder url to any existing Info Item, then Synchronize the Info item to link or store the contents (including subfolders if you have the Include subfolders when importing or syncing folders checkbox checked, found at Tools | Options | Import (more) <tab>). The steps to add a URL attribute to an existing Info Item are found here.
Note: For files located in the same folder or a subfolder of the .urd file, when imported or synchronized, the path will be stored in the URL attribute as a relative path (relative to the location of the .urd file), allowing the .urd file and synchronized files to be relocated to different paths or drives intact.
Note: Available in Professional edition only.