The most common and most likely answer to this crossword clue is the 4 plus 6 letter word EXIT PERMIT
I've seen this crossword clue in The Guardian
E
X
I
T
P
E
R
M
I
T
More clues leading to the result EXIT PERMIT
Buddy explains!
The straight part
We know that "document someone going may need" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case document someone going may need = exit permit.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.