Which version of Adobe Acrobat are you using? (DC, XI, X).
Here's a couple of things to try (for Adobe Acrobat DC):
- Press F8 to Show or Hide the Toolbar at the top of the document window.
- To reset the Toolbars to their default press Alt/Option+F8
- Press Shift+F4 to Show or Hide the Tools pane on the right side of the document window).
- To access all of the different tools, and manage them display the Tools centre (normally you'd click on Tools at the top of the document window to display these) choose Edit > Manage Tools. From here you can open different tool sets or add a toolset to the Tools pane for easy access.
If all of this fails, try restoring the preferences for Acrobat DC: