If you just have got a flat windows installation files in hand and want to create a bootable Windows ISO DVD, you can do that using Windows Assessment and Deployment Kit (ADK)
- oscdimg.exe– A command line CD-ROM and DVD-ROM pre-mastering utility to create bootable ISOs of Microsoft Windows.
And you will get it once you’ll install ADK
You can download it from here, for instance:
For Windows 8: from here
For Windows 8.1: from here
For Windows 10: from here\
- The flat windows installation files