The first thing you should do is upgrade to the last version of Snow Leopard, OS 10.6.8. You can get the OS 10.6.8 Combo Updater from here:
https://support.apple.com/kb/DL1399?locale=en_USJust make sure that any third party software you use is compatible with OS 10.6.8.
Secondly, Adobe no longer provides support for OS 10.6.x and OS 10.7.x:
https://blogs.adobe.com/documentcloud/acrobat-and-reader-support-ending-for-mac-os-x-10-6-and-10-7/Be that as it may, I believe this is where you would start to get the version of Adobe Reader (which is free; Adobe Acrobat is not free) you need:
https://get.adobe.com/reader/