請問光碟遺失,要如何下載安裝CS5?How do I download and install CS5 if my adobe CD is lost?

If you have ordered CS5 directly from Adobe then goto https://account.adobe.com/orders  

You'll prompted to sign in. After you logged in your orders will be showed. There you already can download the installation fies. 

You can also try here: https://prodesigntools.com/all-adobe-cs5-direct-download-links.html

Otherwise you have to contact Adobe directly for a download link. Have your serial number and details of original purchase available. Make it clear that you doesn't need support for an older product but need a download link. Click the link below and scroll down the page to Individual “Sign in to contact us” It should be possible to start an on-line chat with an Adobe agent. 

https://helpx.adobe.com/support.html