Check out my blog where I explain how to create a Custom Document Understanding Model in OCI, using a simple step-by-step approach.
https://blogs.oracle.com/analytics/post/create-a-custom-document-understanding-model-in-oci
To extract customer-specific text from a large number of documents, read this blog to learn how to register and invoke custom document understanding models in OAC.
https://blogs.oracle.com/analytics/post/register-and-invoke-custom-document-understanding-models-in-oac