Can I create subfolders in the Document Sync folder?

The ForeFlight documents feature does not support sub-folders or directories within a binder.  However, you can create folders within your Dropbox or Amazon sync folder and add other Binders for better organization.  Folders will help you organize documents within the sync folder itself.  The folder names will appear as headings in the Documents Catalog and help to better organize the documents within the catalog.
Image 1:  How sub-folders looks within main sync folder of DropBox.
Image 2:  How subfolders within Dropbox or Amazon look within the ForeFlight Documents Catalog.
Once you have your DropBox folders set up, you can create binders to better organize your content.  To create a binder, select the dropdown in the middle, tap on the (+) button in the upper right of the dropdown, enter the binder name, and select SAVE.
Image 3.  Create a binder to match the folders in your Dropbox.  In this example, "Aircraft Documents" is used.

Once your binder is created, tap on it and then tap on CATALOG in the upper right corner.  Tap on your Dropbox line and download the documents you would like in this binder.

Image 4.  Download the documents you want into your binder.  In this example, the "Citation Encore Plus AFM" will be downloaded.

Once downloaded, you will find the document(s) in your binder.

Image 5.  Document is downloaded to binder for better organization.

Adding documents found in the smart binder to another binder does not cause the documents to be re-downloaded or consume extra space on the iPad.