Greetings from Syncfusion.
At present we do not have support for “Toolbar customization using PDF Viewer in Xamarin”, so we cannot hide or remove the annotation toolbar button from the built-in toolbar.
We have added this feature request to our database. You can now track the status of this feature request here
At the planning stage for every release cycle, we review all open features and identify features for implementation based on specific parameters including product vision, technological feasibility, and customer interest. Please visit our website periodically for feature related updates.