Q:
Is it possible to set the default value for an annotation, for example the default thickness for the FreeHand annotation?
A:
The annotation tools can be accessed through readerControl and have a defaults property which can be changed. For example:
readerControl.toolModeMap[PDFTron.WebViewer.ToolMode.AnnotationCreateFreeHand].defaults.StrokeThickness = 5;
Other properties that can be set are StrokeColor, FillColor, TextColor, Opacity and FontSize where applicable.