If not, you can download Windows ISO from Microsoft and use Rufus to create a bootable USB drive. So you should have a disk image files for installation when you buy Windows PC.

Is it possible? Of course! Apple hardware supports macOS, Windows, Linux natively, and the whole installing process can be easily done with a built-in app called Boot Camp. To run Rufus on Mac computer, it’s required your Apple computer has dual boot Windows Mac OS installed, in other words, you must install Windows operating system on Mac. Unfortunately, Rufus only supports 32 or 64 bit Windows XP/7/8/10. However, things will be different after reading this post about how to create bootable USB drive for a PC on a Mac. Freeware as Rufus is, it does a good job in making bootable flash drive from ISO images and has benefited millions of users worldwide, not including Mac OS users though. Rufus is quite helpful when you need to install Windows 7/8/10, update BIOS version, reset Windows user password or else.