Instant blow over documents (5)

I believe the answer is:

rapid

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'instant' is the definition.
(thesaurus)

'blow over documents' is the wordplay.
'blow' becomes 'rap' (rap is a kind of blow).
'over documents' becomes 'id' (I can't explain this - if you can you should believe this answer much more).
'rap'+'id'='RAPID'

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(Other definitions for rapid that I've seen before include "Showing pace" , "Electrical connector" , "haste" , "Speedy, quick" , "Quick or swift" .)

I've seen this clue in The Telegraph.

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