Spear papers in river (7)
I believe the answer is:
trident
'spear' is the definition.
(trident is a kind of spear)
'papers in river' is the wordplay.
'papers' becomes 'id' (identification papers).
'in' indicates putting letters inside.
'river' becomes 'trent' (I've seen this before**).
'id' inserted within 'trent' is 'TRIDENT'.
(Other definitions for trident that I've seen before include "spear carried at sea" , "Fork perhaps" , "Pronged spear" , "Submarine-launched ballistic missile" , "A three-pronged spear as wielded by Neptune" .)