Microsoft Word is no small software. It's probably around 10 million lines of code. As for "per locality business rules differ that's why so many lines of code

Microsoft Word is no small software. It's probably around 10 million lines of code. As for "per locality business rules differ that's why so many lines of code.." seems like you can have a policy engine+DSL (JSON or YAML or custom policy language and engine) thus your code base shouldn't balloon to almost 100 million limes of code...