ProDesignTools is safe. The person who runs the website is an Adobe Community Professional and has permission from Adobe to post links to the installers. However, Adobe may remove the installers at anytime without notice.
NOTE 1: Pre-CS4 software can no longer be activated because the activation servers were shut down years ago.
NOTE 2: To use CS4, CS5 or CS6, you will need a compatible serial number and an older operating system that can support it. And Creative Suite has not been legally sold since 2017.
NOTE 3: The old installers are not compatible with Education or Volume licenses. Only individual licenses will work.
NOTE 4: Be sure to follow the Very Important Instructions on that site or you'll receive an "Access Denied" error.
NOTE 5: Old installers won't work on macOS Sierra or higher without terminal workarounds.
https://helpx.adobe.com/creative-cloud/kb/install-creative-suite-mac-os-sierra.html
NOTE 6: Creative Suite cannot be installed on Catalina or Big Sur as old 32-bit apps are not supported.
Good luck!