Polar supports folders for managing your files in a hierarchy.

We support both basic tags and ‘hierachical’ tags.

Regular tags are shown in the document to the right of the document title and hierarchical tags are shown in the left pane/sidebar.

You can also select tags just on a specific folder for further filtering:

The annotations view also supports the folder setup. The main difference is that you’re now filtering by annotations and not documents and the counts per folder are different (annotations vs documents).