Call this from Edit > Tools > Measure and choose Area Tool from the drop-down list. A dialog box with three tabs appears; make choices in the Settings and Mark up panels, then draw a set of lines line over an object in the PDF whose area you want to measure. Click to change line direction and double-click to close the shape.
View tab
Measurement shows:
Distance: As you are drawing the current edge of a polygon, this dynamically shows its length so far.
Angle: This shows the angle of the first line section related to the X axis; for following line sections it shows the angle relative to the previous section. No signs or directions of rotating are considered.
Area: The area of the polygon is displayed when the drawing is completed.
In the Cursor Location area, the X and Y coordinates of the current cursor position are dynamically displayed relating to the start points of the current line section. No signs are considered.
Setting tab
Perpendicular Measurement sets your lines to be drawn orthogonally (at right angles relative to the X or Y axis).This does not affect lines already drawn, nor concern the last automatically drawn edge of the polygon. You can change this option midway during a measurement.
Units Settings allow you to set the scaling for your measurement. See under Distance tool dialog box. A scale that is set applies to all measuring tools until it is changed.
In the Snap Settings area you can specify that your measuring should snap to points, edges or arcs in your document. Adjust snap sensitivity and color.
Markup tab
Use Markup: Choose this to store the current and future measurements with your PDF document, otherwise all results are lost as soon as you start a new measurement. Enter a text into the text field to appear in a pop-up comment window when you hover the cursor over any line in the shape.
Measuring Color: Sets the color for your measuring lines.