This .NET class wraps the AcDbHandle ObjectARX class. 

The Handle class is the ObjectARX class designed to encapsulate the 64-bit integer handle identifiers that have been in AutoCAD for several releases before R13. A handle uniquely identifies an DBObject within a single database and is saved with that object in the database so that it persists from session to session. Handles are not unique across databases, however. In fact, duplication across databases is almost a certainty, since all databases start with the same hand seed value of 1 and go up from there.

Public Structure Handle
End Structure

public struct Handle {
}

If you have a handle and want the objectId of the object it goes to, then you need to use the Database.GetObjectId() function. 

If you have an objectId and want to get the handle of the object it identifies, then you need to open the object and use its DBObject.GetHandle() function.