Add 1:100 Scale to AutoCAD Plan

I have an architectural drawing saved as an AutoCAD DWG that was set up without a proper scale reference. I simply need the entire file adjusted so every element measures accurately at 1 : 100 when printed or viewed. You may either recalibrate the existing drawing units or apply a viewport-based scale—whichever keeps dimensions true and avoids distortion.

Please work directly in AutoCAD (the plan was created there) and return a clean DWG ready for plotting, along with a quick PDF proof so I can verify accuracy before final sign-off.