You can get it anywhere in internet for you choice, but I strongly recommend you download Windows ISO from official Microsoft website.
For example, if you need to create Windows 10 USB drive, look for ISO here:
You need only:
- Push the "Download Tool Now" button for downloading small Microsoft tool that can give you necessary ISO
- Launch application and assept License Terms
- Choose "Create installation media for another PC" and click "Next"
- Set Language, Edition and Architecture of operation system which you are looking for, then click "Next". On this step you can leave "Use the recomended options for this PC" checked and get Windows ISO exactly for install to your computer
- Select "ISO file" radio-button and clicking "Next" you will start downloading...
* You certainly can select "USB flash drive" on fifth step, and in this case, Microsoft application will force you to reformat the memory stick...
Good News! It's not necessarily for me! )
Why it's better to use official Microsoft official site?
- Malware is impossible
- Trusted publisher :)
- Always actual distributions
- Always actual description
- Lots of information available
- And so on...