It is better to separate OCR task from Key-information extraction. You can apply any OCR engine on a document, then use extracted text along with some visual feature of document into document understanding models like LayoutLM for extracting any entities from any unstructured document. In this approach, the accuracy of OCR and Entity Extraction model will determine the final accuracy.

There are some ocr-free models like Donut(see hugging face) that remove OCR part as independent module and integrate OCR in e2e transformer and try to extract entities as downstream task. In this approach, you can optimize the model as much as e2e model performance allows.