Use Puppeteer’s asynchronous Page.pdf() method to render each HTML document, then await the jobs together with Promise.all() or a concurrency-limited worker pool. This produces one PDF per HTML input. If you need a single combined PDF, add a PDF merge step or combine the content into one HTML document before rendering.
What “asynchronously” means for Puppeteer PDF generation
Puppeteer’s Page.pdf() returns a promise that resolves to PDF bytes. You can await several independent render jobs without writing them as a serial sequence. That does not guarantee that parallel rendering will be faster: each open page uses browser and host resources, so throughput depends on the documents and the machine running Chromium.
There is an important output distinction. Page.pdf() renders a page; it does not automatically join PDFs made from several HTML inputs. With separate inputs, the straightforward result is a collection of PDF files. A combined deliverable requires another step: merge those files with a PDF library, or first build one HTML document containing the material in the required order and render that document once.
Render multiple HTML strings into separate PDFs
The example below uses an array of HTML strings, creates a page for each one, and writes each returned PDF buffer to disk. It uses a bounded worker pool rather than opening a page for every input at once. Save it as render-html.mjs, install Puppeteer in the project, then run node render-html.mjs.
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import puppeteer from 'puppeteer';
import { writeFile } from 'node:fs/promises';
const documents = [
{ name: 'first', html: '<!doctype html><html><body><h1>First report</h1></body></html>' },
{ name: 'second', html: '<!doctype html><html><body><h1>Second report</h1></body></html>' },
];
const concurrency = 3;
const outputs = new Array(documents.length);
let nextIndex = 0;
const browser = await puppeteer.launch();
try {
async function worker() {
while (true) {
const index = nextIndex++;
if (index >= documents.length) return;
const { name, html } = documents[index];
const page = await browser.newPage();
try {
await page.setContent(html, { waitUntil: 'networkidle0' });
const pdf = await page.pdf({
format: 'A4',
printBackground: true,
waitForFonts: true,
});
outputs[index] = pdf;
await writeFile(`${name}.pdf`, pdf);
} finally {
await page.close();
}
}
}
await Promise.all(
Array.from({ length: Math.min(concurrency, documents.length) }, () => worker()),
);
} finally {
await browser.close();
}
console.log(`Rendered ${outputs.length} PDFs.`);In a JavaScript file, the HTML strings contain ordinary HTML markup; the entities shown inside the code block represent angle brackets for publication display. The browser is launched once and reused, while each job gets its own page. The page closes even if loading or PDF creation fails, and the browser closes after the worker pool settles. Set concurrency based on measurements on the actual host rather than assuming that more simultaneous pages are always better.
Choose the failure policy deliberately
With the worker code above, if a job rejects, Promise.all() rejects and the outer finally closes the browser. Other already-running workers may still finish their current work, but the batch is treated as failed. For a workflow that must keep successful PDFs when one input is bad, catch errors inside each worker, record the input name and error, and continue; report the failures separately instead of silently presenting a partial batch as complete.
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Render HTML files from disk
For files, read each input as UTF-8 and pass its contents to page.setContent(). The rest of the page lifecycle is the same. For example, replace the in-memory documents definition with:
import { readFile } from 'node:fs/promises';
const inputPaths = ['input/one.html', 'input/two.html'];
const documents = await Promise.all(
inputPaths.map(async (path, index) => ({
name: `document-${index + 1}`,
html: await readFile(path, 'utf8'),
})),
);Relative asset paths need special care. HTML passed through setContent() does not automatically acquire the same base URL that it would have when opened from its original file location. If the document references local images, stylesheets, or scripts by relative path, use absolute paths or set an appropriate base URL in the HTML, and make sure Chromium can access the resources. If the files rely on browser state such as authentication, configure that state for the pages before loading them.
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Choose load completion and print styling
Wait for the resources the document actually needs
The example waits for networkidle0 before printing, which is useful when external assets need time to load. It may be unsuitable for pages that keep network connections active. Select the page.setContent() wait condition to suit the document; if an important element signals readiness more reliably, wait for that selector before calling page.pdf(). A timeout or rejected load should be surfaced as a per-document failure, not converted into an apparently valid PDF.
Print media and screen media are different
PDF generation uses print media by default. That means print-specific CSS may apply, and screen-only styling may not appear as it does in a browser tab. If the desired output is the screen design, call await page.emulateMediaType('screen') before page.pdf(). For a print document, leave the default media in place and inspect the print styles.
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Set PDF options to match the document
Puppeteer’s documented defaults include Letter paper, no printed background graphics, font waiting enabled, and a 30-second PDF timeout. The sample explicitly chooses A4, enables backgrounds, and keeps font waiting on. Review the installed version’s PDFOptions API for paper dimensions, orientation, margins, page ranges, scale, headers and footers, transparency, and timeout behavior.
- Use
printBackground: truewhen the PDF must retain background colors or images. - Use
preferCSSPageSize: truewhen the document’s CSS@pagesize should take precedence over the API’s format or dimensions. - Use explicit margins or page ranges when the output must follow a defined print layout.
- For more faithful print colors, the Puppeteer documentation notes the CSS property
-webkit-print-color-adjust.
One PDF per file or one combined PDF?
Choose the output structure before implementing the batch. Separate files are simplest when each HTML file represents a report, invoice, or other independently consumed document. Preserve the input order in the result array if you later merge outputs: asynchronous jobs may finish in a different order, but the example stores each output at its original index.
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If one combined PDF is required, either merge the generated PDF byte arrays in a dedicated PDF-processing stage or compose a single HTML document and call page.pdf() once. A single HTML document is convenient when page breaks, shared headers, and consistent styling can be controlled in HTML. A merge stage is appropriate when the inputs must stay separate or have already been rendered. Puppeteer’s page PDF method does not perform that merge itself.
Parallel rendering, reliability, and resource use
A page per input is easy to reason about, and independent jobs can be awaited with Promise.all(). An unbounded Promise.all(documents.map(...)) can, however, open too many pages for a large batch. Use a worker pool or another bounded scheduler and tune its limit against the memory and CPU available on the machine. The Puppeteer documentation does not provide a universal concurrency setting or a throughput guarantee.
Reuse one browser for a batch and close every page after its render. Put browser shutdown in a finally block so failures do not leave a long-running process holding browser resources. If pages should not share cookies or cache, use separate browser contexts; Puppeteer documents that separate browser contexts do not share those values. If the documents need common authentication or cookies, configure them in the context used by their pages.
Troubleshooting common failures
- PDF is blank or missing images: the page may have been printed before its content or external assets finished loading. Choose an appropriate wait condition, wait for a required selector, and confirm that referenced assets are reachable from Chromium.
- Styles differ from the browser view: PDF rendering uses print media by default. Use
emulateMediaType('screen')before printing only when screen styling is the intended output; otherwise correct the print CSS. - Background colors or images are absent: background printing is off by default. Set
printBackground: true. - Paper size or pagination is unexpected: the default format is Letter. Set the desired format, dimensions, margins, or CSS page-size preference explicitly and inspect the
@pagerules. - Fonts appear late or differently: font waiting is enabled by default, but the font resources still need to load successfully. Check the font URLs and allow sufficient time for external resources.
- Large batches become slow or fail under load: reduce the worker count and observe the host’s memory and CPU use. No concurrency value is best for every input set or host.
- Some PDFs exist but the batch exits with an error: one rendering promise may have rejected. Log failures with their input names and decide whether the workflow should fail as a whole or retain successful outputs with an explicit failure report.
- Several PDFs were created but the recipient expects one: add a merge stage, or render a composed HTML document. Multiple calls to
Page.pdf()do not produce a combined document automatically.
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Official Puppeteer references
- Puppeteer PDF generation guide
- Puppeteer Page.pdf() API
- Puppeteer PDFOptions API
- Puppeteer Browser.createBrowserContext() API
- Puppeteer Browser API
These API references identify Puppeteer version 25.12.0 in the cited results; check the documentation matching your installed release because method details and defaults can change.
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