Controlling File Downloads PDF Viewer

28 Feb 20266 minutes to read

The PDF Viewer exposes a downloadStart event that enables interception of a document download before it begins. Use this event to apply custom logic and, if needed, cancel the download by setting the event’s cancel flag.

Using the downloadStart Event

The downloadStart event fires immediately before the download process starts. The event handler receives a DownloadStartEventArgs object (for example, args) that exposes properties such as cancel and fileName which can be used to inspect or stop the download.

<template>
  <div id="app">
    <ejs-pdfviewer id="pdfViewer" ref="pdfviewer" :documentPath="documentPath" :resourceUrl="resourceUrl"
      :downloadStart="downloadStart">
    </ejs-pdfviewer>
  </div>
</template>

<script setup>

import {
  PdfViewerComponent as EjsPdfviewer, Toolbar, Magnification, Navigation,
  LinkAnnotation, BookmarkView, Annotation, ThumbnailView,
  Print, TextSelection, TextSearch, FormFields, FormDesigner, PageOrganizer
} from '@syncfusion/ej2-vue-pdfviewer';
import { provide } from 'vue';

const resourceUrl = "https://cdn.syncfusion.com/ej2/31.2.2/dist/ej2-pdfviewer-lib";
const documentPath = "https://cdn.syncfusion.com/content/pdf/pdf-succinctly.pdf";

provide('PdfViewer', [Toolbar, Magnification, Navigation, LinkAnnotation, BookmarkView, Annotation,
  ThumbnailView, Print, TextSelection, TextSearch, FormFields, FormDesigner, PageOrganizer])

const downloadStart = function (args) {
    // Your custom logic here
    args.cancel = true; // Prevent download action
}

</script>
<template>
  <div id="app">
    <ejs-pdfviewer id="pdfViewer" ref="pdfviewer" :documentPath="documentPath" :resourceUrl="resourceUrl"
      :downloadStart="downloadStart">
    </ejs-pdfviewer>
  </div>
</template>

<script>

import {
  PdfViewerComponent, Toolbar, Magnification, Navigation,
  LinkAnnotation, BookmarkView, Annotation, ThumbnailView,
  Print, TextSelection, TextSearch, FormFields, FormDesigner,
  PageOrganizer } from '@syncfusion/ej2-vue-pdfviewer';

export default {
  name: "App",
  components: {
    "ejs-pdfviewer": PdfViewerComponent
  },
  data() {
    return {
      resourceUrl: "https://cdn.syncfusion.com/ej2/31.2.2/dist/ej2-pdfviewer-lib",
      documentPath: "https://cdn.syncfusion.com/content/pdf/pdf-succinctly.pdf"
    };
  },
  provide: {
    PdfViewer: [Toolbar, Magnification, Navigation, LinkAnnotation, BookmarkView, Annotation,
      ThumbnailView, Print, TextSelection, TextSearch, FormFields, FormDesigner, PageOrganizer]
  },
  methods: {
   downloadStart: function (args) {
      // Your custom logic here
      args.cancel = true; // Prevent download action
    }
  }
}
</script>
<template>
  <div id="app">
    <ejs-pdfviewer id="pdfViewer" ref="pdfviewer" :documentPath="documentPath" :serviceUrl="serviceUrl"
      :downloadStart="downloadStart">
    </ejs-pdfviewer>
  </div>
</template>

<script setup>

import {
  PdfViewerComponent as EjsPdfviewer, Toolbar, Magnification, Navigation,
  LinkAnnotation, BookmarkView, Annotation, ThumbnailView,
  Print, TextSelection, TextSearch, FormFields, FormDesigner,
  PageOrganizer } from '@syncfusion/ej2-vue-pdfviewer';
import { provide } from 'vue';

const serviceUrl = "https://document.syncfusion.com/web-services/pdf-viewer/api/pdfviewer";
const documentPath = "https://cdn.syncfusion.com/content/pdf/pdf-succinctly.pdf";

provide('PdfViewer', [Toolbar, Magnification, Navigation, LinkAnnotation, BookmarkView, Annotation,
  ThumbnailView, Print, TextSelection, TextSearch, FormFields, FormDesigner, PageOrganizer])

const downloadStart = function (args) {
    // Your custom logic here
    args.cancel = true; // Prevent download action
}

</script>
<template>
  <div id="app">
    <ejs-pdfviewer id="pdfViewer" ref="pdfviewer" :documentPath="documentPath" :serviceUrl="serviceUrl"
      :downloadStart="downloadStart" >
    </ejs-pdfviewer>
  </div>
</template>

<script>

import {
  PdfViewerComponent, Toolbar, Magnification, Navigation,
  LinkAnnotation, BookmarkView, Annotation, ThumbnailView,
  Print, TextSelection, TextSearch, FormFields, FormDesigner,
  PageOrganizer } from '@syncfusion/ej2-vue-pdfviewer';

export default {
  name: "App",
  components: {
    "ejs-pdfviewer": PdfViewerComponent
  },
  data() {
    return {
      serviceUrl: "https://document.syncfusion.com/web-services/pdf-viewer/api/pdfviewer",
      documentPath: "https://cdn.syncfusion.com/content/pdf/pdf-succinctly.pdf"
    };
  },
  provide: {
    PdfViewer: [Toolbar, Magnification, Navigation, LinkAnnotation, BookmarkView, Annotation,
      ThumbnailView, Print, TextSelection, TextSearch, FormFields, FormDesigner, PageOrganizer]
  },
  methods: {
    downloadStart: function (args) {
       // Your custom logic here
       args.cancel = true; // Prevent download action
    }
  }
}
</script>

By default, the cancel argument is false, so the download proceeds unless the handler explicitly sets args.cancel = true.

Enhanced Flexibility

Using the downloadStart event enables conditional control over downloads—for example, to enforce authentication, restrict downloads for certain documents, or prompt users for confirmation. When using server-backed viewers, confirm whether server-side behavior requires additional handling; canceling the client-side event prevents the local download but may not affect server workflows.