# Tune performance for large documents

> Keep page rendering responsive, choose a layout, and measure representative DOCX workflows.



SuperDoc virtualizes paginated documents by default. Keep that baseline until measurements from representative DOCX files show a specific scrolling, memory, loading, or worker-startup problem.

## Tune the page window deliberately [#tune-the-page-window-deliberately]

The default paginated window is five pages with one overscan page. Set it explicitly only when comparing a measured alternative:

```ts
const superdoc = new SuperDoc({
  selector: '#editor',
  document: '/large-contract.docx',
  layoutEngineOptions: {
    virtualization: {
      enabled: true,
      window: 5,
      overscan: 1,
    },
  },
  onPaginationUpdate: ({ totalPages }) => {
    pageCount.textContent = String(totalPages);
  },
});
```

A larger window can reduce repaints during fast scrolling while keeping more pages mounted. A smaller window reduces mounted work but can make navigation less smooth. Change one value at a time and measure on the devices and documents the product supports.

## Choose print or web layout [#choose-print-or-web-layout]

Paginated print layout preserves page boundaries and uses page virtualization. Web layout reflows semantic content to the container and does not provide headers, footers, rulers, or page-count updates.

Use `viewOptions: { layout: 'web' }` with `layoutEngineOptions: { flowMode: 'semantic' }` for the continuous surface. [Build a responsive Editor layout](/editor/built-in-ui/responsive-layout) compares the two layouts and their host sizing requirements.

## Control worker startup [#control-worker-startup]

Keep the default 30-second `workerStartupTimeoutMs` unless measurements show that the worker bundle needs more time to download or evaluate. Use `workerUrls` when the application must serve the document, collaboration, and review-index module workers from explicit same-origin URLs.

Worker load errors fail immediately; increasing the timeout does not repair a missing file, blocked Content Security Policy, or invalid worker response. See [Secure integration](/editor/secure-integration) for the browser boundary.

## Measure the whole task [#measure-the-whole-task]

Test opening, first interaction, scrolling, editing, collaboration, and export with representative DOCX files. Record document size and page count with the result so a regression can be reproduced.

> **Verification target (success)**
>
> On the slowest supported device, open a representative large DOCX, scroll from start to end, edit text on distant
> pages, and export. No action should lose document state or leave controls permanently busy.