We have a very strange front door to our new office in that it can only be opened and closed with a key.

I'd like to replace this system with a proper door handle, keeping the key cylinder. I.e. I want to be able to leave the door unlocked to go in and out without leaving the door open.

Does anyone know who or what kind of tradesman I should call for this kind of work? English or German definition is fine - and if you can recommend a company or someone, please let me know. (Zurich City)

Thank you - appreciate your time.

Erm, a locksmith maybe?

"Schlosser" according to leo.org.

Here's a pic of the door.

It's not the lock that we want to change. Would a locksmith be able to fit a proper door handle?

Yes, certainly.