Note to Gerwin is a written note found in The Knife of Dunwall.
I understand your concern about security, but I trust in the security of a key hanging from my own belt, not a combination lock. A combination lock can be guessed, cracked, or bribed. But with a simple lock and key, the contents of my archives remain safe.
As for lockpicks? A fable. I've never known such a thing to truly exist. Have you?
It can be found on a desk in Timsh's office in his estate, across from the chest containing his mother's will.