How to get 2D plans from threejs model

I am working with a website which have a 3d model created in threejs … User can chane length , height and can add doors or windows. As a result the model will be changed automaticly … My mission now is find a way to take 2D plans from the final model which the user changed and save them as pdf later… I have no idea how to do this…
Is it possible to connect this model to Autocad by using AutoCAD Software’s .NET API / C# .NET ? Can this way solve the problem?

Have you considered to use one of the exporters of three.js to export your model to a format that AutoCAD can import? Ideally you use GLTFExporter but if AutoCAD does not support glTF you might want to fallback to STLExporter.