The most common and most likely answer to this crossword clue is the 10 letter word PAGINATION
I've seen this crossword clue in The Sunday Telegraph
P
A
G
I
N
A
T
I
O
N
Buddy explains!
The straight part
We know that "marking numbers on documents" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marking numbers on documents = pagination.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.
What does PAGINATION mean?
PAGINATION noun- The act of creating pages for a document, book, etc., or determining when to truncate text on the pages.
- The act of numbering pages for a document, book, etc.
- The separation of data into batches, so that it can be retrieved with a number of smaller requests.