I am using a Samsung Galaxy S III Smartphone. I think all Andriod Users should have the same interface as I'm seeing so hopefully this works for you too. In Adobe Reader you should see 3 choices "Recents", "Documents" and "What's New" Press "Recents" and then press the Menu Key located bottom left corner on this phone you will then see the option to "Clear Recent Documents" press that and that'll clear your recent document queue.
Hope this helps.
Europe, Middle East and Africa