The estimator opens the PDF sheets, sets the scale and traces or clicks each item. The software totals lengths, areas and counts by item.
On-Screen Takeoff is also the name of a software product. Estimators measure with tools such as On-Screen Takeoff and Bluebeam.
Check the scale on every sheet before you measure. Enlarged plans and details use different scales from the main plans. Name each item clearly so another person can follow your work.
Takeoff Tool reads an On-Screen Takeoff (.ost) file if you add one. It does not measure by tracing.