Highlight fields in PDF

This code sample shows how to mark all fields in a PDF document.

Each field will be highlighted with a colored border. We will use a RectangleShape as the border. The color of the border depends on the type of a field.

C# code sample

// enumerate the pages
foreach (var page in document.Pages)
{
   // enumerate the widgets
   foreach (var widget in page.Widgets)
   {
      //create a highlight shape for each widget
      var highlight = CreateHighlight(widget);

      if (highlight == null) continue;

      //add the highlight to the page
      page.Overlay.Add(highlight);
   }
}

' enumerate the pages
For Each page As var In document.Pages
	' enumerate the widgets
	For Each widget As var In page.Widgets
		'create a highlight shape for each widget
		Dim highlight = CreateHighlight(widget)

		If highlight Is Nothing Then
			Continue For
		End If

		'add the highlight to the page
		page.Overlay.Add(highlight)
	Next
Next

In CreateHighlight routine we create the RectangleShape. The simplest way to create rectangles with different colors is to use conditions(if..else..)

C# code sample

private static Shape CreateHighlight(Widget widget)
{
   //create different pens for different field types 
   Pen pen;
   if (widget.Field is TextField)
   {
      pen = new Pen(System.Drawing.Color.Red, 3);
   }
   else if (widget.Field is CheckBoxField)
   {
      pen = new Pen(System.Drawing.Color.Blue, 3);
   }
   else if (widget.Field is RadioButtonField)
   {
      pen =  new Pen(System.Drawing.Color.Green, 3);
   }
   else if (widget.Field is ValueField)
   {
      pen = new Pen(System.Drawing.Color.Orange, 3);
   }
   else
   {
      pen = new Pen(System.Drawing.Color.Yellow, 3);
   }

   //create a rectangular highlighting
   return new RectangleShape(widget.Left, widget.Bottom,
                              widget.Width, widget.Height, pen);
}

Private Shared Function CreateHighlight(widget As Widget) As Shape
	'create different pens for different field types 
	Dim pen As Pen
	If TypeOf widget.Field Is TextField Then
		pen = New Pen(System.Drawing.Color.Red, 3)
	ElseIf TypeOf widget.Field Is CheckBoxField Then
		pen = New Pen(System.Drawing.Color.Blue, 3)
	ElseIf TypeOf widget.Field Is RadioButtonField Then
		pen = New Pen(System.Drawing.Color.Green, 3)
	ElseIf TypeOf widget.Field Is ValueField Then
		pen = New Pen(System.Drawing.Color.Orange, 3)
	Else
		pen = New Pen(System.Drawing.Color.Yellow, 3)
	End If

	'create a rectangular highlighting
	Return New RectangleShape(widget.Left, widget.Bottom, widget.Width, widget.Height, pen)
End Function

Another way is to implement a custom field visitor inherited from the FieldVisitor class.

internal class MarkFieldVisitor : FieldVisitor
{
   public override object Visit(TextField field, object argument)
   {
      //we passed the widget as argument;
      var widget = argument as Widget;
      var pen = new Pen(Color.Red, 3);
      return CreateHighlight(widget, pen);
   }

   public override object Visit(CheckBoxField field, object argument)
   {
      //we passed the widget as argument;
      var widget = argument as Widget;
      var pen = new Pen(Color.Blue, 3);
      return CreateHighlight(widget, pen);
   }

   public override object Visit(RadioButtonField field, object argument)
   {
      //we passed the widget as argument;
      var widget = argument as Widget;
      var pen = new Pen(Color.Green, 3);
      return CreateHighlight(widget, pen);
   }

   public override object Visit(ValueField field, object argument)
   {
      //we passed the widget as argument;
      var widget = argument as Widget;
      var pen = new Pen(Color.Orange, 3);
      return CreateHighlight(widget, pen);
   }

   public override object Visit(Field field, object argument)
   {
      //we passed the widget as argument;
      var widget = argument as Widget;
      var pen = new Pen(Color.Yellow, 3);
      return CreateHighlight(widget, pen);
   }

   private static object CreateHighlight(Widget widget, Pen pen)
   {
      return new RectangleShape(widget.Left, widget.Bottom,
                                 widget.Width, widget.Height, pen);
   }
}

Friend Class MarkFieldVisitor
	Inherits FieldVisitor
	Public Overrides Function Visit(field As TextField, argument As Object) As Object
		'we passed the widget as argument;
		Dim widget = TryCast(argument, Widget)
		Dim pen = New Pen(Color.Red, 3)
		Return CreateHighlight(widget, pen)
	End Function

	Public Overrides Function Visit(field As CheckBoxField, argument As Object) As Object
		'we passed the widget as argument;
		Dim widget = TryCast(argument, Widget)
		Dim pen = New Pen(Color.Blue, 3)
		Return CreateHighlight(widget, pen)
	End Function

	Public Overrides Function Visit(field As RadioButtonField, argument As Object) As Object
		'we passed the widget as argument;
		Dim widget = TryCast(argument, Widget)
		Dim pen = New Pen(Color.Green, 3)
		Return CreateHighlight(widget, pen)
	End Function

	Public Overrides Function Visit(field As ValueField, argument As Object) As Object
		'we passed the widget as argument;
		Dim widget = TryCast(argument, Widget)
		Dim pen = New Pen(Color.Orange, 3)
		Return CreateHighlight(widget, pen)
	End Function

	Public Overrides Function Visit(field As Field, argument As Object) As Object
		'we passed the widget as argument;
		Dim widget = TryCast(argument, Widget)
		Dim pen = New Pen(Color.Yellow, 3)
		Return CreateHighlight(widget, pen)
	End Function

	Private Shared Function CreateHighlight(widget As Widget, pen As Pen) As Object
		Return New RectangleShape(widget.Left, widget.Bottom, widget.Width, widget.Height, pen)
	End Function
End Class

The visitor we can use in the CreateHighlight method:

private static Shape CreateHighlight(Widget widget)
{
   var fieldVisitor = new MarkFieldVisitor();
   return widget.Field.Accept(fieldVisitor, widget) as Shape;
}

Private Shared Function CreateHighlight(widget As Widget) As Shape
	Dim fieldVisitor = New MarkFieldVisitor()
	Return TryCast(widget.Field.Accept(fieldVisitor, widget), Shape)
End Function

The input PDF:

The result: