Set up measurement tools

When creating a new instance of PDF.js Express, the enableMeasurement property needs to be set to true to display the measurement annotation tools in the UI.

WebViewer({
  ... // other options
  enableMeasurement: true
}, viewerElement);

Besides passing in a constructor option, measurement can be toggled using the PDF.js Express API with the enableMeasurement and disableMeasurement functions.

WebViewer({
  ... // other options
}, viewerElement)
  .then((instance) => {
    instance.enableFeatures([instance.Feature.Measurement]);
  });

WebViewer({
  ... // other options
}, viewerElement)
  .then((instance) => {
    instance.UI.enableFeatures([instance.UI.Feature.Measurement]);
  });