WinCC V7.3 was a milestone in the "Classic" WinCC line, known for: Scalability: Supporting everything from single-user systems to complex Client/Server architectures Integration:
At least 1.5 GB for installation and up to 10 GB for working projects. Key Installation Notes siemens wincc 73 exclusive download
If you are looking for this specific version, here is the official way to handle it: Official Access and Updates Trial Downloads: WinCC V7