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Use PDF.js’s display API to load a document, obtain a page, create a viewport, size a canvas, and await the page’s render task. Configure a separate PDF.js worker from the exact same version as the display package, and run your app through HTTP rather than file://. The example below uses the current stable release label v6.3.289 shown on the PDF.js getting-started page on September 29, 2026; check the project’s releases before pinning a production dependency.
Which PDF.js layer should you use?
PDF.js has a core layer, a display layer, and a complete viewer. Core parses and interprets PDF files, but the project describes that API as advanced and likely to change. The display layer exposes the practical browser API for rendering pages and reading document information. The viewer is a ready-made interface built on that layer and can be used as a starting point when you need search, thumbnails, navigation, and other controls.
For a custom canvas viewer, install the pdfjs-dist distribution package or use an official prebuilt release. Pin the display package and worker to one version. Package paths can differ between bundlers and releases, so verify the path against the version you install.
Minimal browser setup
Install and expose the module
With npm:
npm install pdfjs-distThe following example assumes a modern bundler that can import the display module and worker module. If your bundler requires a copied worker asset or a URL, follow its worker-asset instructions and point workerSrc at that deployed file.
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Render one page
import * as pdfjsLib from 'pdfjs-dist/build/pdf.mjs';
import workerUrl from 'pdfjs-dist/build/pdf.worker.mjs?url';
pdfjsLib.GlobalWorkerOptions.workerSrc = workerUrl;
const canvas = document.querySelector('#pdf-canvas');
const context = canvas.getContext('2d');
const pdfUrl = '/documents/example.pdf';
async function renderPage(pageNumber = 1) {
const loadingTask = pdfjsLib.getDocument({ url: pdfUrl });
const pdf = await loadingTask.promise;
const page = await pdf.getPage(pageNumber);
const scale = 1.5;
const viewport = page.getViewport({ scale });
const outputScale = window.devicePixelRatio || 1;
canvas.width = Math.floor(viewport.width * outputScale);
canvas.height = Math.floor(viewport.height * outputScale);
canvas.style.width = `${Math.floor(viewport.width)}px`;
canvas.style.height = `${Math.floor(viewport.height)}px`;
const transform = outputScale !== 1
? [outputScale, 0, 0, outputScale, 0, 0]
: null;
await page.render({
canvasContext: context,
transform,
viewport
}).promise;
}
renderPage().catch(console.error);Add the target canvas to your page:
<canvas id="pdf-canvas" aria-label="PDF page"></canvas>The sequence is deliberate: getDocument returns a loading task; its promise resolves to a PDF document; getPage resolves to a page; getViewport calculates geometry; and page.render returns a render task that must finish before you reuse the canvas.
Canvas size, zoom, and HiDPI output
The viewport’s dimensions are CSS-sized page dimensions at your chosen scale. A high-DPI display needs more backing-store pixels than CSS pixels. Multiply the canvas’s width and height attributes by devicePixelRatio, keep the CSS dimensions at the unmultiplied viewport size, and pass the same output scale as a render transform. This keeps text sharp without making the page occupy twice the layout space on a 2× display.
A larger scale increases detail but also increases canvas memory and drawing work. The official example’s 1.5 scale is a demonstration value, not a universal setting. You can recalculate the viewport when a user changes zoom, then resize and rerender the canvas.
Rotation and page geometry
page.getViewport({ scale, rotation }) includes page dimensions, scale, and initial rotation. Use the viewport dimensions for both the backing store and CSS sizing; do not hard-code letter or A4 dimensions because PDFs can contain pages of different sizes.
Loading data instead of a URL
getDocument accepts a URL or PDF data held in memory. A URL is convenient when the browser can fetch the file directly. For an upload flow, obtain an ArrayBuffer and pass it as data:
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const file = document.querySelector('#pdf-file').files[0];
const data = new Uint8Array(await file.arrayBuffer());
const loadingTask = pdfjsLib.getDocument({ data });
const pdf = await loadingTask.promise;In either mode, retain the returned document while navigating pages. Destroy a document when your component is removed or when a new file replaces it, so worker and document resources can be released.
Multiple pages and navigation
Render only the page currently visible, or a small window around it, rather than creating full-resolution canvases for an entire document. PDF.js’s FAQ notes that the demo viewer creates, renders, and holds canvases only for visible pages to reduce memory use.
let pdfDocument;
let currentRenderTask;
let currentPage = 1;
async function openDocument(url) {
const task = pdfjsLib.getDocument({ url });
pdfDocument = await task.promise;
currentPage = 1;
await drawCurrentPage();
}
async function drawCurrentPage() {
if (currentRenderTask) {
currentRenderTask.cancel();
}
const page = await pdfDocument.getPage(currentPage);
const viewport = page.getViewport({ scale: 1.25 });
const canvas = document.querySelector('#pdf-canvas');
const context = canvas.getContext('2d');
canvas.width = viewport.width;
canvas.height = viewport.height;
canvas.style.width = `${viewport.width}px`;
canvas.style.height = `${viewport.height}px`;
currentRenderTask = page.render({ canvasContext: context, viewport });
try {
await currentRenderTask.promise;
} finally {
currentRenderTask = null;
}
}
async function nextPage() {
if (currentPage < pdfDocument.numPages) {
currentPage += 1;
await drawCurrentPage();
}
}Wait for the current render before drawing another page into the same canvas. If navigation can be clicked rapidly, cancel the previous render and ignore its cancellation error before starting the newly requested page.
Worker configuration and browser constraints
Keep the worker version identical
The worker is a separate deployment asset. The display library and worker must come from the exact same PDF.js version. A stale cached worker, a CDN worker from another release, or a mismatched copied file can produce an API/worker version mismatch. Pin both assets, update them together, and clear the old worker from your asset cache when upgrading.
Use an HTTP server
The worker is not enabled for pages opened directly with file://. Start your development server and open the application at an HTTP or HTTPS origin. This also gives you realistic fetch and module behavior.
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Cross-origin PDFs
Browser same-origin rules apply to the PDF request. If the PDF is hosted on another origin, configure that server to send an appropriate CORS header or fetch it through an application-server proxy. A PDF URL that works when pasted into a browser can still fail when requested by your web app if CORS is absent. The generic/demo viewer also restricts this functionality when deployed outside the project’s own domain.
Range requests
PDF.js may use HTTP range requests to retrieve portions needed for visible pages, depending on browser support and the server’s response headers. Your server should correctly handle range requests and return coherent content-length and range responses; otherwise loading may fall back to a complete download or fail for a misconfigured response.
Useful implementation choices
| Choice | Use it when | Trade-off |
|---|---|---|
| Higher scale | Readers need sharper zoomed text | More backing-store memory and render work |
| Render on demand | Documents have many pages or users navigate selectively | Lower memory, with work when a page becomes visible |
| Pre-render pages | A short document must feel instantly navigable | Higher memory and startup cost |
| URL input | The browser can securely fetch a hosted PDF | Requires correct CORS, server responses, and network access |
| In-memory data | The user uploads a file or your app already fetched bytes | Your code must handle upload, validation, and data lifetime |
| Full viewer | You want a complete interface quickly | Less control over layout and application integration |
| Custom display UI | You need application-specific controls and styling | You must build navigation, accessibility, and lifecycle behavior |
These are design axes, not controlled performance benchmarks. Measure with the page sizes, devices, and navigation patterns your application actually supports.
Troubleshooting
“API version does not match the Worker version”
Confirm that the installed pdfjs-dist version and deployed worker are identical. Inspect the worker URL in browser developer tools, remove stale service-worker or CDN caches, and redeploy both files together.
Nothing works when opening the HTML file
Serve the app through your development server. Do not test worker-based rendering from a file:// URL.
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Failed to fetch or CORS errors
Check the PDF request’s origin and response headers. Enable CORS on the PDF host or proxy the request through your own server. Confirm that authentication headers or cookies are forwarded as required.
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Blank canvas or an unexpectedly large page
Ensure the canvas backing dimensions use viewport dimensions multiplied by the output scale, while CSS dimensions use the unmultiplied viewport. Set the canvas size before calling render, and verify that your context and viewport belong to the same page.
Pages consume too much memory
Stop retaining canvases for every page. Render visible pages on demand, discard pages that leave the viewing window, and avoid unnecessarily high scales.
Navigation draws an older page over a newer one
Do not reuse a canvas until the previous render task has completed. Cancel an in-flight task when supported, handle its cancellation, and serialize page changes.
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Example using cURL (see the ScreenshotNeo documentation):
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import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)Node.js:
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
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Frequently Asked Questions
Can PDF.js render a PDF without its full viewer?
Yes. The display API is intended for custom integrations; the full viewer is optional.
Does PDF.js automatically make every PDF cross-origin request work?
No. The PDF server must permit the browser request with CORS, or your application must proxy the file.
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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Is v6.3.289 a permanent version recommendation?
No. It was the stable label shown on the getting-started page on September 29, 2026. Check current releases and compatibility guidance before upgrading or publishing a new integration.
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