Hi dear friend, I’m using Dorico 4 pro and I’m so happy. But I would like to solve this problem. Can I remove the key signature only some instruments such as horns in Fa in the full score? Because if I write, for example, a score in E major I see in the horn’s part the 4 key signatures instead of to see nothing. Thanks a lot for the collaboration.
Antonello. 
In Setup you can use Dorico’s “no key sig” horns:
You can also use an independent key sig for an existing instrument. At the beginning, click that staff and use Shift+K to input a key sig, type “open” then the hold down the Alt key when you hit Enter. Alt+Enter makes it independent to that staff.
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Just to clarify – independent key signatures aren’t intended for replicating transposing scores. By default Dorico’s full scores are concert pitch, but you can change this to transposed pitch if you like; and in transposed pitch scores, you’ll see that key signatures automatically update correctly on staves belonging to transposing instruments.
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