Can I use the S5/S7 for Windows software with a 840C/840D CNC Controller?

Yes, it is possible to program the Sinumerik 840C/840D CNC controller using the S5/S7 for Windows programming software. 

The 840C CNC controller acts like an S5 PLC and the 840D CNC controller acts like an S7 PLC that can manage the large CNC program files.

More information about S5/S7 for Windows and other IBH products can be found here.