Documents quietly placed on copiers (6)
I believe the answer is:
papers
'documents' is the definition.
(I've seen this before)
'quietly placed on copiers' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'placed on' means one lot of letters go next to another.
'copiers' becomes 'apers' (ape can mean to mimic or copy).
'p'+'apers'='PAPERS'
(Other definitions for papers that I've seen before include "Documents; the press" , "tabloids, maybe" , "Documentation" , "ID etc." , "Identifying documents" .)