@Goyal, Mayank If you are developing a custom form recognizer model then using a storage connection to place your training dataset in a Azure storage container and generating a SAS URL is a pre-requisite to develop a model.
After the model is developed you can use the custom model or the pre-built model to pass the form as a URL or stream to get the results. In case of URL you need to ensure the form is available on public internet and if the form is on azure storage container you can restrict access by using a SAS URL and other options available to expire the token after a certain period.