Hi
Most Mac applications come in self-contained packages (ctrl-click, or right-click, & you will see Show Package Contents), they can just be dragged to the trash.
Some applications have their own uninstaller which must be run.
With Adobe Reader 8, I believe the icon in Applications is a folder so just drag it to the trash & empty the trash. I believe Download Manager (Applications/Utilities) should be the same. Someone may know different.
There is also
AppZapper or
AppDelete. These work by you dragging & dropping the application you wish to delete onto its icon, AppZapper/AppDelete then pulls all parts of that application together then moves it to the trash.
Steve