The Measure Tools enable you to measure distances and areas of objects in PDF documents. The measure tools are especially useful when you need to know the distances or areas associated with objects in a form or computer-aided design (CAD) drawing or when you want to measure certain areas of a document before sending to a professional printer. The measure tools are available to users only if the PDF creator enables measuring functionality.
When you use a measure tool, the tool dialog box displays the measurements of the line segments you draw. If you want to set the default measurement unit, please choose File > Preferences > Measuring > the desired unit in the Measurement Units group before using any measure command.