This is the 16608th most frequent Russian word.
секретностью
"Секретностью" means "secrecy" or "confidentiality."
In this sentence, 'секретностью' refers to the manner in which the documents should be handled, emphasizing the need for confidentiality and discretion.
Эти документы должны быть защищены с максимальной секретностью.
These documents must be protected with maximum secrecy.
Here, 'секретностью' indicates the quality or state related to the confidentiality of the plan and the actions taken to preserve it.
Секретностью этого плана занимаются специальные службы.
The secrecy of this plan is handled by special agencies.
In this sentence, 'секретностью' is used to express the concept of maintaining discrete and confidential handling of the matter as part of a trusted relationship.