You can use the Highlighter command to call attention to specific parts of a page, just as you would use a colored marker to highlight an important paragraph or key phrases in a document or report.
Display the page in the Image View window.
On the Annotation ribbon, choose Highlighter.
The pointer changes to a highlighting marker when you move it over
the item.
Draw a horizontal line
to highlight a text line, or hold down the left mouse button and drag
the marker across the area you want to highlight.
Release the mouse button to drop the highlighting mark on the item.
Choose Highlighter
in the Annotation Tools group, then 
Color
in the Annotation Settings group to change the default highlighting color
(yellow). Then, select the color you want to use for future highlights.
It does not affect existing highlights. To change the color of a currently
selected highlight, right-click the highlight and select Color
from the shortcut menu.