In contrast to criminal, papers are legally acceptable (5)
I believe the answer is:
valid
'legally acceptable' is the definition.
(I've seen this before)
'in contrast to criminal papers' is the wordplay.
I cannot really see how this works, but
'papers' could be 'id' (short for identification papers) and 'id' is found within the answer.
The remaining letters 'val' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'are' acts as a link.
Can you help me to learn more?
(Other definitions for valid that I've seen before include "Officially acceptable" , "Legitimate" , "Effectual" , "Sound and logical, also legal" , "Legally acceptable and sound" .)