You create a data source, a skillset, and an index. These three components become part of an indexer that pulls each piece together into a single multi-phased operation.
Note: At the start of the pipeline, you have unstructured text or non-text content (such as image and scanned document JPEG files). Data must exist in an Azure data storage service that can be accessed by an indexer.
Indexers can "crack" source documents to extract text from source data.
References:
https://docs.microsoft.com/en-us/azure/search/cognitive-search-tutorial-blob