The most common and most likely answer to this crossword clue is the 7 letter word SCRIBED
I've seen this crossword clue in Independent
S
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Buddy explains!

The straight part
We know that "put pen to paper" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case put pen to paper = scribed.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 SCRIBED mean?
SCRIBED verb- To write.
- To write, engrave, or mark upon; to inscribe.
- To record.
- To write or draw with a scribe.
- To cut (anything) in such a way as to fit closely to a somewhat irregular surface, as a baseboard to a floor which is out of level, a board to the curves of a moulding, etc.; so called because the workman marks, or scribes, with the compasses the line that he afterwards cuts.
- To score or mark with compasses or a scribing iron.