Nonsense documents containing double Dutch should receive criticism (12)
I believe the answer is:
fiddlesticks
'nonsense' is the definition.
(I've seen this before)
'documents containing double dutch should receive criticism' is the wordplay.
'documents' becomes 'files'.
'containing' indicates putting letters inside.
'double dutch' becomes 'dd' (this could be a standard abbreviation of which I'm unaware).
'should receive' means one lot of letters goes inside another.
'criticism' becomes 'stick' (I've seen this before).
'files' enclosing 'dd' is 'fiddles'.
'fiddles' going around 'stick' is 'FIDDLESTICKS'.
(Other definitions for fiddlesticks that I've seen before include "Expression of annoyance or disagreement" , "Blast!" , "Rhubarb" , "Bilge" , "Bother!" .)