Do you print your drawings so that you can measure off them?
Open the drawing in QuickScale and click on either end of a known measurement (eg door width). This will scale the PDF for you automatically. From then on, click on either end of the lengths and areas that you want to measure and QuickScale will calculate the dims and show them to you on the drawing.
You can try this free - please click on this link https://www.quickscale.co/trial.html