Extend Selection Mode is a keyboard method of anchoring the cursor before you select text. Pressing F8 turns it on and and pressing any arrow keys at that point will select text from the anchor point in that direction. In the following illustration the anchor point is where the arrow indicates, and the down arrow was pressed a few times.

Notice that the Status Bar indicates that you’re in Extend Selection mode. (In versions of Word earlier than 2007, the status bar indicates EXT.) Pressing the Escape key will take you out of Extend Selection mode.

When you press F8 to begin Extend Selection mode and press F8 again immediately after, Word will select one full word. Pressing F8 again will select the entire sentence. Pressing F8 a fourth time will select an entire paragraph and pressing F8 a fifth time will select the entire document.

You can use Extend Selection mode along with the Advanced Find feature to select text between an anchor point and a particular word.  In the following example, the anchor point was set at the beginning of a paragraph and then Advanced Find was selected.  The text “Bach” was entered into the Find what box.

When the Find Next button was clicked, this was the result:

Extend Selection mode is an alternate way to quickly select text.