My client still use Live Cycle Designer ES4. I need to install SP1, but I can't find a link to download it. I know that Adobe doesn't support ES4 anymore, but is there some way to download and install SP1?
Sounds like your client has the license for LiveCycle Designer ES4 and they might also have the SP1 install kit to give to you. There is no official download site where you can get that these days. If you own a license, then the Adobe Electronic Software Download (ESD) or https://experience.adobe.com/#/downloads/ may have these files. Your client could also contact support and ask for the files.