Woof
1. Start acrobat reader
2. Select Help>About Plug-ins>Acrobat Forms
3. hold in Control+Alt+Shift and click on the credits button.

Whale sound in Adobe Acrobat 4.0
1. Open Adobe Acrobat 4.0
2. Go to Help>About Plug-ins>Acrobat Annotations
3. Hold down Ctrl and left-click on Credits
4. You will then hear the sound of a whale, see the Plug-in logo change to a whale, and see the Credits button change to Harpoon.