Extract and Highlight Text in Blazor PDF Viewer Component

5 Dec 20244 minutes to read

The Syncfusion® Blazor PDF Viewer component provides powerful capabilities to extract text from a PDF document and highlight specific text. This functionality enables users to interactively process PDF content, making it easier to emphasize important information.

To extract text, the PDF Viewer utilizes the FindText method, which identifies the positions of specified text within the PDF. Once the text is found, user can highlight it by creating a highlight annotation and adding it asynchronously using the AddAnnotationAsync method.

The following code example demonstrates how to extract text from a PDF document and highlight it in the Syncfusion® Blazor PDF Viewer component.

@page "/"
@using Microsoft.Extensions.Caching.Memory
@using Syncfusion.Blazor.Popups;
@using Syncfusion.Blazor.Buttons;
@using Syncfusion.Blazor.Navigations;
@using Syncfusion.Blazor.SfPdfViewer;
@using System.Drawing;
@using Syncfusion.Pdf.Parsing;
@using Syncfusion.Pdf;

@inject IJSRuntime jsRuntime
@inject IMemoryCache MemoryCache

<button @onclick="loadDocument">Extract Text</button>
<button @onclick="highlightText">Highlight Text</button>

<SfPdfViewer2 @ref="viewer" Height="100%" DocumentPath="@DocumentPath"
              Width="100%" IsExtractText="true">
    <PdfViewerEvents DocumentLoaded="OnDocumentLoaded"></PdfViewerEvents>
</SfPdfViewer2>

@code {
    SfPdfViewer2 viewer;
    private string DocumentPath { get; set; } = "wwwroot/data/pdf-succinctly.pdf";
    private Dictionary<int, List<Syncfusion.Drawing.RectangleF>> matchRects = new Dictionary<int, List<Syncfusion.Drawing.RectangleF>>();

    public async void loadDocument()
    {
        using (FileStream docStream = new FileStream(Path.GetFullPath("wwwroot/data/pdf-succinctly.pdf"), FileMode.Open, FileAccess.Read))
        {
            // Load the PDF document.
            PdfLoadedDocument loadedDocument = new PdfLoadedDocument(docStream);

            // Find the text and store its positions.
            loadedDocument.FindText("the", out matchRects);
        }
    }

    public async void highlightText()
    {
        if (matchRects != null && matchRects.Count > 0)
        {
            var targetText = matchRects.FirstOrDefault(target => target.Value.Count > 0);

            if (targetText.Key > 0)
            {
                PdfAnnotation pdfAnnotation = new PdfAnnotation
                {
                    Type = AnnotationType.Highlight,
                    PageNumber = targetText.Key
                };

                List<Bound> newBounds = new List<Bound>();
                Bound newBound = new Bound
                {
                    X = ConvertPointToPixel(targetText.Value[0].X),
                    Y = ConvertPointToPixel(targetText.Value[0].Y),
                    Width = ConvertPointToPixel(targetText.Value[0].Width),
                    Height = ConvertPointToPixel(targetText.Value[0].Height)
                };
                newBounds.Add(newBound);
                pdfAnnotation.Bounds = newBounds;

                await viewer.AddAnnotationAsync(pdfAnnotation);
            }
            else
            {
                // Handle the case where the text was not found
                Console.WriteLine("Text not found for highlighting.");
            }
        }
        else
        {
            Console.WriteLine("No text found to highlight.");
        }
    }

    private void OnDocumentLoaded()
    {
        // This method can be used to perform actions once the document is loaded, if needed.
    }

    private float ConvertPointToPixel(double number)
    {
        return (float)(number * (float)96 / 72);
    }
}

View sample in GitHub.