Insubstantial collection of documents about newspaper (7)
I believe the answer is:
fragile
'insubstantial' is the definition.
(thesaurus)
'documents about newspaper' is the wordplay.
'documents' becomes 'file' (file can mean a collection of documents).
'about' indicates putting letters inside.
'newspaper' becomes 'rag' (informal term for a newspaper).
'file' enclosing 'rag' is 'FRAGILE'.
'collection of' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for fragile that I've seen before include "Delicate, tenuous" , "Liable to break easily" , "To be handled with care" , "Brittle" , "Easily broken or damaged" .)