This is the most important point. Software that hasn’t been updated since the Windows XP era was not built for modern security threats. Downloading an old .exe from an unknown source is a leading cause of malware, ransomware, and keyloggers. You have no way of knowing if the file has been modified to include a virus.
Use an open-source converter like OpenBabel (free, command-line based) to translate the file into a modern format, then open it in one of the tools above. Isis Draw 2.4 Free Download
Isis Draw was a popular, lightweight chemical structure drawing program used in the late 1990s and 2000s. Version 2.4 was one of its last stable free releases. This is the most important point