First of documents to bring up is dull (5)
I believe the answer is:
drear
'dull' is the definition.
(I've seen this before)
'first of documents to bring up' is the wordplay.
'first of' suggests taking the first letters.
'to bring up' becomes 'rear' (rearing is a kind of bringing up).
The first letter of 'documents' is 'd'.
'd'+'rear'='DREAR'
'is' acts as a link.
(Other definitions for drear that I've seen before include "grave" , "Grim" , "Cheerless (literary)" , "Poetic dull and uninteresting" , "Dismal (literary)" .)