What did you download, exactly? Was it Acrobat Pro (please check).
If it was Acrobat Pro, what often happens is that people install Acrobat Pro but KEEP RUNNING ADOBE READER.
Stop doing that, and you get to use the trial.
If you are not sure which one is running please do one of these
* look in the title bar (Windows)
* look at the app name next to the apple icon in the menu bar (Mac)
* tell us what you see in the TOOLS area (just the top headers will do).