- Select Measure > Distance in the Comment tab to measure the distance between two points. While measuring the distance, you can specify whether to show the default leader on both side of the measurement points or not in Measuring Preferences. Click the first point, move the pointer to the second point, and click again. If you choose to use the default leader, move your mouse to determine the leader length, and then click on the document again to finish measuring. The measurements will appear on the page.
- Select Measure > Perimeter in the Comment tab to measure a set of distances between multiple points. Click the first point to start, and then click each point you want to measure. Double-click the last point to end measuring. (Tip: When you move the cursor to a position toward the first point, a small red circle will appear at the first point, which allows you to click on the first point to end measuring and measure a closed perimeter.)
- Select Measure > Area of Polygon in the Comment tab to measure the area within the line segments that you draw. Click the first point to start, and then click each point you want to measure. After you have clicked at least two points, click the first point or double-click the last point to complete the area measurement.
- Select Measure > Area of Circle in the Comment tab to measure the area of circular objects in PDF files. Click and drag to draw an oval (or use Shift + drag to draw a circle) across the object that you want to measure, and release your mouse to complete measuring.
Note: When measuring with the Distance, Perimeter, or Area of Polygon command, you can hold down SHIFT to snap the two points horizontally, vertically, or diagonally (in 45 degrees). You can also choose to complete or cancel measurement by right-clicking the measurement and choosing options from the context menu.
After you select the measuring tool, the Format tab appears in the right panel, which allows you to calibrate the scale ratio, snap measurement, export measurement markup, etc.
If your PDF file includes embedded scale ratio, you can measure distance/perimeter/area using the embedded scale ratio. Before that, you need to select the Use Scale and Units From Document (When present) option in File > Preferences > Measuring. Then all the following measuring will use the embedded scale ratio. To calibrate the scale ratio for your document for an accurate result, choose either method of the following:
- With the Use Scale and Units From Document (When present) option selected:
1) Choose Calibrate
from the Format tab and then click the two points of the line whose actual length has already been known. (Tips: When drawing, you can hold down SHIFT to snap the two points horizontally, vertically, or diagonally. You can also click Snap to Paths 
in the Format tab to capture the path in the page.)2) When the second point is selected, the Calibration dialog box pops up.
3) Type the actual length that the line represents and choose the appropriate unit, which will set a new scale ratio.
4) (Optional) If you already have the correct scale ratio, directly define the measurement value and choose the appropriate unit in the Format tab.
5) Then in the pop-up Calibration dialog box, click Store Scale in Page to apply the new scale ratio to the current page, or click Apply to All Pages to apply it to all pages (Or click the
/
icon in the Format tab to apply the new scale ratio to the current page or all pages). The new scale ratio will be embedded into the page or all pages respectively, replacing the original embedded scale ratio.6) As the scale ratio is embedded into the document, the measurements in the document change accordingly.
- With the Use Scale and Units From Document (When present) option unselected, directly define a custom scale ratio in the Format tab, or click Calibrate
in the Format tab to define a new scale ratio. The defined scale ratio will only be applied to the current page.
- Check Show result information in the Format tab if you want to see the current measuring result, including real distance, angle, horizontal and vertical position, etc.
- CheckMeasurement markup in the Format tab to add and show the measurement lines you draw in the PDF file. When this option is checked, you can add a label to measurement markups either by using the one specified in measuring preferences or inputting a new one in the Add Label box. The label for Distance markup will be shown in the distance measurement line, while the label for Perimeter and Area markups will be shown in their pop-up notes. When you put the pointer over the measurement markups with the Hand command selected, you can also view the measurement result and label.
- Check Rulers in the Format tab to show the rulers.
Choose one or more snapping types from the Format tab. For precise measurements, position the key points when moving the cursor.
Snap to Endpoints
: a small red circle will appear at the endpoint of the path when moving the cursor toward the end of the path.Snap to Midpoints
: a small red triangle will appear at the midpoint of a path when moving the cursor over the path.Snap to Paths
: the cursor will automatically change to a red square box on a path when moving the cursor over the path.Snap to Intersections
: a small red cross will appear at the intersection of two paths when moving the cursor over the point of two intersecting paths. - Choose Export to Excel
from the Format tab to save all the measurement information in your PDF to a CSV file.
Note: The object you draw will disappear when the Measurement Markup is deselected in the Distance dialog box.