Windows might tell you that you can't open it, or in the worst case, you might encounter a OAB file related error message.
Before you can open a OAB file, you'll need to figure out what kind of file the OAB file extension refers to.
In Exchange 2013, OAB is processed by mailbox server role which owns the copy of the database of the Arbitration system mailbox with OAB Persisted Capabilities.
OAB resides on the mailbox server in the folder “C:\Program Files\Microsoft\Exchange Server\V15\Client Access\OAB”.
The database can freely move to other mailbox servers if part of a DAG and the OAB files will be generated immediately for clients to download.