A long time ago, in a valley far, far away, Adobe Acrobat had one-button keyboard shortcuts to common tools. Much like cousins Photoshop, Illustrator, InDesign, and most other Adobe applications, pressing H on the keyboard activated the Hand Tool in Acrobat, Z the Zoom Tool, and so on. No longer. Now, in Acrobat versions 6 and 7, Standard, Professional, or Reader, pressing H, Z, I, T, V, and all the rest do nothing. Nada. Zip. Bupkiss.
If you want the Select Tool (for selecting text to copy within a PDF), you must select it from the colorful toolbar. Other tools… Well, Acrobat has many, many toolbars, with most hidden in the default install.
Fortunately, there is a simple way to restore the single-button shortcuts to activate the most common Acrobat tools. In Preferences (CMD+K/CTRL+K), go to the General pane and check Use Single-Key Accelerators to Access Tools. Fixed. Now all the familiar shortcuts work, and the valley is safe from needless, Carpal Tunnel-inducing trips to toolbars after trips to nested menus to show those toolbars.