we have looked into this recently, and it is currently not possible to directly address the DocuWare REST API from the Power Platform. This is mostly due to the authentication at DocuWare which is currently based on cookies. For the Power Platform there is the need for oAuth 2 Authentication, but oAuth is not yet available for the DocuWare API.
Additionally you have to make the DocuWare On-Premises system open to the Internet to be able to communicate with it.
All of this drives us to creating a connector on Power Automate for DocuWare Cloud only
So, I think there should be some kind of different integration, maybe you can create index files using DocuWare Control (https://support.docuware.com/de-de/knowledgebase/article/KBA-36502
) and save them on some folder which is synced locally and then DocuWare Import imports these documents. Also you could use Webhooks to send information from DocuWare to a webhook on the Power Platform and process it there. Maybe also an integration with AutoIndex will work. And maybe you will be able to use the API once DocuWare has oAuth 2 enabled, but this needs to be developed first.