Avoid third-party "WinCC Viewer RT download" websites offering cracked or standalone installers. They often contain malware, will fail Siemens audits, and provide zero technical support.
If your company has purchased a license for WinCC Professional, you likely received a USB stick or a DVD set with the software. The "WinCC Viewer RT" installer is located inside the main setup folder of these delivery media. You do not need to download it separately if you have the physical media. wincc viewer rt download