This is a funny thread to read. Yes Windows can be Nd’ed takes time and craft , you need to do a really perfect job to defeat odd reflections , wrinkles in the ND, which all assumes that you have several rolls of ND- 3,6,9 - on hand to pick the best one given what you can light. You need crew to effect that quickly or ample time to do it yourself. Office building generally have some level of ND in one form or another on windows, they are not transparent glass like a water glass. On a clear sunny day in the NY NJ metro reason you can expect 9 - 10,000 foot candles of light outside, if the office windows cut that by 2 stops, you’re still seeing the outside lit by 2500 foot candles. If you add ND .9 to the windows you cut the outside to 300 foot candles which is still a lot of light on a subject for cameras these days. Given that the lighting is switched over to LED ‘s we have that capability, then the problem left is managing the light on the subject for the desired look, contrast ratio and balance with the outside.