Applying Category to multiple documents

[Machetta]

There is a page in the WIKI but it is not helpful

I don't understand this line:
Execute the action add category will be shown a popup.

When I select (using checkboxes) multiple documents, right-click them, the "Add category" item is greyed out in the context menu.

[jllort]

This feature actually is only included in professional version. In nearly future will be available in community too.