The most common and most likely answer to this crossword clue is the 8 letter word UNVOICED
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More clues leading to the result UNVOICED
Buddy explains!

The straight part
We know that "On paper only" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case on paper only = unvoiced.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 UNVOICED mean?
UNVOICED adjective- Not spoken or expressed.
- Spoken without vibration of the vocal chords.
- (of a signal) That does not contain voice.
- Of an IRC user: not granted voice privileges.