You can use Snap to expand windows vertically, which can be especially helpful for reading longer documents.
Drag the edge of the window to the top or bottom of the screen to expand the window to the entire height of the desktop. The width of the window doesn't change.
To return the window to its original size, drag the title bar away from the top of the desktop, or drag the bottom edge of the window away from the bottom of the desktop.
Snap might not work on some programs that have custom window behaviors.