To integrate the document intelligence model into an existing Azure AI Search solution, you should add the model as a custom skill to the existing Azure AI Search service. This will allow you to configure the model to extract the required data from the documents and make it available for search and indexing. Option A is incorrect because creating a new Azure AI Search service is not necessary if you already have an existing service in place. Option C is incorrect because Azure Logic Apps are not required for this integration, as the custom skill can be added directly to the Azure AI Search service. Option D is incorrect because creating a new Azure Cognitive Services resource is not the appropriate approach for implementing the document intelligence model as a custom skill in Azure AI Search.