Control PDF Annotations Visibility in PDF Viewer

1 Jan 20255 minutes to read

Overview

This guide demonstrates how to control the visibility of PDF annotations in documents loaded and saved using the Syncfusion PDF Viewer in TypeScript. This process allows the annotations to be visible only in the Syncfusion PDF Viewer.

How to Control Annotation Visibility

Step 1: Follow the steps provided in the link to create a simple PDF Viewer sample.

Step 2: Add Buttons for Annotation Modification and Downloading

Include buttons in your HTML for annotation modification and downloading the PDF.

<button id="save">Download</button>
<div id="PdfViewer"></div>

step 3: Add the following code snippet to add annotations to the PDF document. You can also include other annotations as needed.

const viewer: PdfViewer = new PdfViewer({
    documentPath: 'https://cdn.syncfusion.com/content/pdf/annotations-v1.pdf',
    resourceUrl: "https://cdn.syncfusion.com/ej2/28.1.33/dist/ej2-pdfviewer-lib",
});

// Append the PdfViewer to the DOM
viewer.appendTo('#PdfViewer');

viewer.documentLoad = function (args) {
    //Code snippet to add basic annotations. You can also include other annotations as needed.
        viewer.annotation.addAnnotation("Highlight", {
            bounds: [{x: 97, y: 610, width: 350, height: 14}], 
            pageNumber: 1
        } as HighlightSettings);
        viewer.annotation.addAnnotation("Underline", {
            bounds: [{x: 97, y: 723, width: 353.5, height: 14}],
            pageNumber: 1
        } as UnderlineSettings);
        viewer.annotation.addAnnotation("Strikethrough", {
            bounds: [{x: 97, y: 836, width: 376.5, height: 14}],
            pageNumber: 1
        } as StrikethroughSettings);
    }

Step 4: Add Event Listeners for Button Clicks

Attach event listeners that handle annotation visibility modifications and downloading the document.

// Add event listener to the button with ID 'download'
document.getElementById('save')?.addEventListener('click', save);

Step 5: Modify Annotation Flags Function

Implement a function that changes the annotation visibility settings for the document.

// Import PdfAnnotationFlag and PdfDocument from the Syncfusion PDF library. 
import { PdfAnnotationFlag, PdfDocument } from '@syncfusion/ej2/pdf';

// Function to get Base64 of the loaded document and modify annotation flags
function save() {
  // Assuming pdfviewer is globally accessible or a part of another object
  viewer.saveAsBlob().then((blob: Blob) => {
    const reader = new FileReader();
    reader.onload = function () {
      let base64data = reader.result as string;

      // Extract base64 string from Data URL
      const base64EncodedData = base64data.split('base64,')[1];

      // Create a PdfDocument instance with base64 data
      const document1 = new PdfDocument(base64EncodedData);

      // Modify flag for each annotation
      for (let i = 0; i < document1.pageCount; i++) {
        const page = document1.getPage(i);
        for (let j = 0; j < page.annotations.count; j++) {
          const annot = page.annotations.at(j);
          // Set flag to noView
          annot.flags |= PdfAnnotationFlag.noView;
        }
      }

      // Save modified document as a blob
      document1.saveAsBlob().then((modifiedBlob: { blobData: Blob }) => {
        const internalReader = new FileReader();
        internalReader.onload = function () {
          const modifiedBase64 = internalReader.result as string;

          // Create a link to download the modified PDF
          const downloadLink = document.createElement('a');
          downloadLink.href = modifiedBase64;
          downloadLink.download = 'modified.pdf';
          downloadLink.click();
        };
        internalReader.readAsDataURL(modifiedBlob.blobData);
      });
    };
    reader.readAsDataURL(blob);
  });
}

By following these steps, the annotations in a PDF document can be set to be visible in the Syncfusion PDF Viewer, providing control over annotation visibility based on different platforms.

View sample in GitHub