I'm not sure ISO is the right format you're looking for, as that is used for optical discs. There are several paid and free solutions to clone a hard drive to a virtual machine.
This is normally done via a harddrive cloning utility. User friendly products include Paragon, EaseUS, and a host of others. If you're comfortable with a limited interface or command-line solution, Clonezilla or even dd are standard utilities for this.
If you are running the cloning process on the PC you want to clone, you will need to either use the bundled startup software or boot using a live image to avoid booting into Windows so that the disk may be copied in its entirety. You can "convert" any format that is created by the software you choose by booting into a virtual machine the same way and going through the steps to restore the drive.
Note that there may be a lot more set up involved if you intend on booting the cloned harddrive in a virtual machine. Making the OS behave like it used to can be tricky in a virtual environment. Windows will not only expect certain drivers to be there that aren't, but also core software and components will be configured to use the original hardware. It's likely the system will blue screen on boot, and it's usually easier to simply use it as a secondary disk.