Call this from Edit > Tools > Measure and choose Perimeter 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 or a closed shape over an object in the PDF whose perimeter you want to measure. Click to change line direction, click to confirm the last line, then right-click and choose Complete Measurement from the shortcut menu to finish drawing and measuring an open shape, or double-click to have the program add the last line to close the shape.
View tab
Measurement shows:
Distance: As you are drawing the current section of a set of lines it 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.
Perimeter: The total length of the line set is dynamically displayed as you are drawing it. If you use a shortcut menu to complete drawing with an open shape, the total line set length is shown. If you double-click to form a polygon, its perimeter is shown.
In Cursor Location, 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 allows 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.