Rectangle Annotation (Shape) in Blazor SfPdfViewer Component

12 May 20268 minutes to read

Rectangle annotations let users highlight regions, group content, or draw callout boxes on PDFs for reviews and markups. The Blazor SfPdfViewer allows you to add rectangles from the toolbar, customize appearance, edit/delete them in the UI, and export them with the document.

Rectangle overview

Enable Rectangle Annotation in the Viewer

Rectangle annotations are available by default in the Blazor SfPdfViewer component with the annotation toolbar enabled.

Add Rectangle Annotation

Add Rectangle Annotation Using the Toolbar

Rectangle annotations can be added from the annotation toolbar:

  1. Select Edit Annotation in the viewer toolbar to open the annotation toolbar.
  2. Select Shape Annotation to open the shape list.
  3. Choose Rectangle to enable rectangle drawing mode.
  4. Click and drag on the PDF page to draw the rectangle.

Shape toolbar

NOTE

When the viewer is in Pan mode and a shape drawing mode is activated, the viewer switches to Text Select mode.

Enable Rectangle Mode

Switch the viewer into rectangle drawing mode using SetAnnotationModeAsync.

@using Syncfusion.Blazor.Buttons
@using Syncfusion.Blazor.SfPdfViewer

<SfButton OnClick="OnClick">Rectangle Annotation</SfButton>
<SfPdfViewer2 DocumentPath="@DocumentPath"
              @ref="viewer"
              Width="100%"
              Height="100%">
</SfPdfViewer2>

@code {
    SfPdfViewer2 viewer;
    public async void OnClick(MouseEventArgs args)
    {
        await viewer.SetAnnotationModeAsync(AnnotationType.Rectangle);
    }
    private string DocumentPath { get; set; } = "wwwroot/Data/PDF_Succinctly.pdf";
}

Add Rectangle Programmatically

Use the AddAnnotationAsync method to add a rectangle annotation at a specific location. Ensure the document is loaded and the component reference is available before invoking this method.

@using Syncfusion.Blazor.Buttons
@using Syncfusion.Blazor.SfPdfViewer

<SfButton OnClick="@AddRectangleAsync">Add Rectangle Annotation</SfButton>
<SfPdfViewer2 Width="100%" Height="100%" DocumentPath="@DocumentPath" @ref="@Viewer" />

@code {
    SfPdfViewer2 Viewer;
    public string DocumentPath { get; set; } = "wwwroot/Data/Shape_Annotation.pdf";

    public async void AddRectangleAsync(MouseEventArgs args)
    {
        PdfAnnotation annotation = new PdfAnnotation();
        // Set the Rectangle annotation type
        annotation.Type = AnnotationType.Rectangle;
        // Page numbers start from 0. So, if set to 0 it represents page 1.
        annotation.PageNumber = 0;

        // Bound of the rectangle annotation
        annotation.Bound = new Bound();
        annotation.Bound.X = 200;
        annotation.Bound.Y = 480;
        annotation.Bound.Width = 150;
        annotation.Bound.Height = 75;
        // Add rectangle annotation
        await Viewer.AddAnnotationAsync(annotation);
    }
}

Customize Rectangle Appearance

Configure default rectangle appearance (fill color, stroke color, thickness, opacity) during control initialization using RectangleSettings. These settings apply when rectangles are created from the toolbar or programmatically.

@using Syncfusion.Blazor.SfPdfViewer

<SfPdfViewer2 @ref="@viewer"
              DocumentPath="@DocumentPath"
              RectangleSettings="@RectangleSettings"
              Width="100%"
              Height="100%">
</SfPdfViewer2>

@code {
    SfPdfViewer2 viewer;
    private string DocumentPath { get; set; } = "wwwroot/Data/PDF_Succinctly.pdf";

    PdfViewerRectangleSettings RectangleSettings = new PdfViewerRectangleSettings
    {
        FillColor = "yellow",
        Opacity = 0.9,
        StrokeColor = "#ff6a00",
        Thickness = 2
    };
}

Manage Rectangle (Edit, Move, Resize, Delete)

Edit Rectangle

Edit Rectangle (UI)

  • Select a rectangle to view resize handles.
  • Drag any side/corner to resize; drag inside the shape to move it.
  • Edit fill, stroke, thickness, and opacity using the annotation toolbar.

Shape tools

Use the annotation toolbar tools to modify:

  • Edit fill Color tool
    Edit fill color

  • Edit stroke Color tool
    Edit stroke color

  • Edit Opacity slider
    Edit opacity

  • Edit Thickness slider
    Edit thickness

Edit Rectangle Programmatically

Modify an existing rectangle annotation programmatically using EditAnnotationAsync. Retrieve the target annotation from GetAnnotationsAsync and update the desired properties before submitting the edit.

@using Syncfusion.Blazor.Buttons
@using Syncfusion.Blazor.SfPdfViewer

<SfButton OnClick="@EditRectangleAsync">Edit Rectangle Annotation</SfButton>
<SfPdfViewer2 Width="100%" Height="100%" DocumentPath="@DocumentPath" @ref="@Viewer" />

@code {
    SfPdfViewer2 Viewer;
    public string DocumentPath { get; set; } = "wwwroot/Data/Shape_Annotation.pdf";

    public async void EditRectangleAsync(MouseEventArgs args)
    {
        // Get annotation collection
        List<PdfAnnotation> annotationCollection = await Viewer.GetAnnotationsAsync();
        // Select the rectangle annotation to edit
        PdfAnnotation annotation = annotationCollection[0];
        // Change the fill color of rectangle annotation
        annotation.FillColor = "#FFFF00";
        // Change the stroke color of rectangle annotation
        annotation.StrokeColor = "#0000FF";
        // Change the thickness of rectangle annotation
        annotation.Thickness = 2;
        // Change the opacity (0 to 1) of rectangle annotation
        annotation.Opacity = 0.9;
        // Edit the rectangle annotation
        await Viewer.EditAnnotationAsync(annotation);
    }
}

Delete Rectangle

The PDF Viewer supports deleting existing annotations through the UI and API.
See Delete Annotation for full behavior and workflows.

Comments

Use the Comments panel to add, view, and reply to threaded discussions linked to rectangle annotations. It provides a dedicated interface for collaboration and review within the PDF Viewer.

Set Properties While Adding Individual Annotations

Set properties for individual rectangle annotations by passing values directly during AddAnnotationAsync.

@using Syncfusion.Blazor.Buttons
@using Syncfusion.Blazor.SfPdfViewer

<SfButton OnClick="@AddMultipleRectanglesAsync">Add Multiple Rectangles</SfButton>
<SfPdfViewer2 Width="100%" Height="100%" DocumentPath="@DocumentPath" @ref="@Viewer" />

@code {
    SfPdfViewer2 Viewer;
    public string DocumentPath { get; set; } = "wwwroot/Data/Shape_Annotation.pdf";

    public async void AddMultipleRectanglesAsync(MouseEventArgs args)
    {
        // Rectangle 1
        PdfAnnotation annotation1 = new PdfAnnotation();
        annotation1.Type = AnnotationType.Rectangle;
        annotation1.PageNumber = 0;
        annotation1.Bound = new Bound() 
        {
            X = 200,
            Y = 480,
            Width = 150,
            Height = 75
        };
        annotation1.Opacity = 0.9;
        annotation1.StrokeColor = "#ff6a00";
        annotation1.FillColor = "#ffff00";
        annotation1.Author = "User 1";

        // Rectangle 2
        PdfAnnotation annotation2 = new PdfAnnotation();
        annotation2.Type = AnnotationType.Rectangle;
        annotation2.PageNumber = 0;
        annotation2.Bound = new Bound() 
        {
            X = 380,
            Y = 480,
            Width = 120,
            Height = 60
        };
        annotation2.Opacity = 0.85;
        annotation2.StrokeColor = "#ff1010";
        annotation2.FillColor = "#ffe600";
        annotation2.Author = "User 2";

        // Add both rectangles
        await Viewer.AddAnnotationAsync(annotation1);
        await Viewer.AddAnnotationAsync(annotation2);
    }
}

Disable Rectangle Annotation

Disable rectangle annotations programmatically or through component settings as needed by your application requirements.

Handle Rectangle Events

The PDF viewer provides annotation life-cycle events that notify when Rectangle annotations are added, modified, selected, or removed.
For the full list of available events and their descriptions, see Annotation Events

Export and Import

The PDF Viewer supports exporting and importing annotations. For details on supported formats and workflows, see Export and Import annotations.

See Also