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: