LDAP works fully for On-Premise. Sync's users pulls there network ID and allows for "Windows Account" login.
LDAP can be used to sync users to the cloud if you use the User Synchronization Desktop app. However, with this method you will not be able to use Windows Account login since it is not available in the same form in the cloud at all v7.2 and prior.
Starting in v7.3, Azure AD is available to use with the cloud to connect on site ad with cloud DocuWare Accounts.
Attached is the basic guide to get that done. It is different than the On-Prem....