Open the Drawing tools drop-down menu in the Comment Toolbar (part of the Main Toolbar) to access drawing tools. Choose from the following:
Line (1)
Choose this tool, click and keep the left mouse button pressed to start drawing a line. Release the mouse to finish.
To resize or rotate a line, choose the 
Hand tool, click the line, then hover the mouse over its endpoint to get this cursor 
and start transforming.
Pencil (2)
Choose this tool then click to draw freehand lines on the PDF.
Properties
Select the Hand tool and right-click on any edge of a drawing object for its shortcut menu. Choose Properties to modify object appearance, view its revision history, or redefine its Author and Subject. Choose Reply to add a Note to the object, or Set Appearance as Default Properties to use the current object’s properties as the norm for all newly drawn objects of the same type.