'Adobe' isn't a program. It's the name of a company that makes lots of different software, so saying that you used to open files in Adobe is a bit like saying that you used to open them in Microsoft. i.e. it doesn't tell us which program (made by Adobe) you were using. At a guess, it might well have been Adobe Reader (which opens pdf documents) but I'll try to provide a generic answer (covering all possibilities) anyway:
It seems that your computer might well have got its 'file associations' mixed up. To fix it, first ensure that you've got a relevant file somewhere on your hard drive. (e.g. if you're trying to open a file sent to you by email, save it to your hard drive, in somewhere like 'My Documents', first).
Then navigate to the location of such a file (any one will do) and RIGHT-click on it. Select 'Open With'. Click on the name of the program you want to use and then ensure that there's a tick next to the box marked 'Always use the selected program to open this kind of file'. It should then open correctly, as will all other files (of the same sort) in future.
(Note: If you don't see the relevant program in the list, or if 'Always use the selected program . . .' isn't present, click on 'Browse'. That will enable you to navigate to the location of the program file and will also ensure that the tick box is shown).