AI automation with Data security

How to create a AI-powered system that will be used to analyze documents submitted by employees, identifying specific structural errors based on defined legal parameters. The system will be made available to all of the client’s employees, who will simply upload their documents and receive an automated assessment in return.

But the data can not be pass or available to any third party it means do not want to share data to a model because of legal regulations they need to respect. what will be best approach to handle this situation ? should need to develop a model from scratch or can use existing Model which can use privately for an orgnaisation only? is it too much costly if use own server for model ? If someone has experties on this please suggest solution on it
Is there any body who has experties in this area and can let us know if it is possible to create such AI project?