> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/web/best-practices/preload-worker-files.md).

# Preloading WebViewer library/worker files

Learn how to optimize WebViewer with the initialDoc option to efficiently load large library resources like PDF or Office workers. Preload workers upfront for seamless file processing and display on s

When WebViewer is loaded with the `initialDoc` option, it will first load the large library resources, like PDF or Office workers, depending on the type of file you are trying to open, and then the file will be processed and displayed on the screen.

By default WebViewer will load the worker files lazily when needed but if WebViewer needs to be initialized without opening a file or if you will be loading both PDF and Office files, you can use the `preloadWorker` option to load the workers up front.

{% hint style="info" %}
It is not recommended to use this option when WebViewer Server is enabled as certain clients (IE, mobile devices) will not want to load the PDF workers at all for performance reasons.
{% endhint %}

{% tabs %}
{% tab title="JavaScript" %}
{% code lineNumbers="true" %}

```js
WebViewer({
  path: '../../../lib',
  preloadWorker: 'pdf',
  ...
}, document.getElementById('viewer'))
  .then(instance => {
      // ...
  });
```

{% endcode %}
{% endtab %}
{% endtabs %}

Here WebViewer is displayed without opening a file but the PDF workers have still been loaded.

![](https://3532544125-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FX9YnTSKIHvV7m0A36LbO%2Fuploads%2Fgit-blob-f130c30c46b678d19d6ca1c5f2726422290bf482%2F1256fc6bdeb8456d579141a7210848daf73554d6-1000x756.png?alt=media)

## Preload MS Office workers

The MS Office workers are preloaded in the same way as PDF workers, you only need to change the `preloadWorker` option to "office". If you decide to preload both PDF and Office workers on the initial load change it to "all".

{% tabs %}
{% tab title="JavaScript" %}
{% code lineNumbers="true" %}

```js
WebViewer({
  path: '../../../lib',
  preloadWorker: 'office', // 'all' to preload both pdf & office workers
  ...
}, document.getElementById('viewer'))
  .then(instance => {
      // ...
  });
```

{% endcode %}
{% endtab %}
{% endtabs %}


---

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