How to install software on old pentium desktop

That will be Nearly Impossible. First you would need to locate old Adobe software that at the time it was available it did NOT depend on OnLine Activation of any kind as all the internet (online) Activation Servers for older Adobe software has been shut down. Now you may get a reply that the activation servers for CS4, 5 and 6 are still available. But those versions of Adobe software probably won't run on computers usiing OLD Pentium CPUs.

If you have a Website and a Friend that is trying to help you in some way with that website then both of you need newer computers to do whatever you want to do with that website.

https://helpx.adobe.com/creative-cloud/system-requirements.html
-Win7 is dead https://www.microsoft.com/en-us/windows/windows-7-end-of-life-support-information
-Win8 is also no longer supported https://support.microsoft.com/en-us/help/4580358/windows-8-1-update