Clear as a document (8)
I believe the answer is:
I believe this is a double definition.
'clear' is the first definition.
('manifest' can be a synonym of 'clear')
'a document' is the second definition.
(manifest is a kind of document)
'as' acts as a link.
(Other definitions for manifest that I've seen before include "Display", "list of passengers flying", "List of ship's cargo or passengers", "Reveal", "Obvious, like ship's cargo list".)