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Convert a URL to PDF in PHP with cURL extension

The baseline job: give the API a URL, get PDF bytes back. One POST, binary response, no callback dance — the body of the response is the file. Everything else on this page is about doing that reliably: auth, error handling, and not treating a JSON error as a PDF.

Below is a complete, runnable PHP program using cURL extension, no third-party dependency needed. It reads your API key from the SNAPDOK_KEY environment variable — free keys take about thirty seconds and need no card.

<?php
$body = json_encode([
    'url' => "https://your-app.com/report/42",
    'format' => "pdf",
]);

$ch = curl_init("https://snapdok.io/v1/render");
$headers = [];
curl_setopt_array($ch, [
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => $body,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_TIMEOUT => 90,
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer ' . getenv('SNAPDOK_KEY'),
        'Content-Type: application/json',
    ],
    CURLOPT_HEADERFUNCTION => function ($ch, $line) use (&$headers) {
        $parts = explode(':', $line, 2);
        if (count($parts) === 2) $headers[strtolower(trim($parts[0]))] = trim($parts[1]);
        return strlen($line);
    },
]);

$bytes = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_RESPONSE_CODE);
curl_close($ch);

if ($status !== 200) {
    throw new RuntimeException("snapdok error $status: $bytes");
}
file_put_contents('page.pdf', $bytes);

The response is the document itself with Content-Type: application/pdf. Errors come back as JSON with an error code — which is why every sample here checks the status before writing bytes to disk: the classic integration bug in every language is saving {"error":"UNAUTHORIZED"...} as report.pdf and discovering it a week later.

PDF rendering uses the page's print stylesheet and reflows to paper width, so the width parameter does not apply to PDFs (it is a screenshot concept). If a page looks wrong as PDF, its @media print CSS is usually the culprit. Repeated identical requests inside 24 hours are served from cache — X-Cache: HIT — and not charged.

Same endpoint, one more trick: if the page you are rendering has a form on it, adding "pdf_forms": true to a PDF render brings it back with real, fillable AcroForm fields — a PDF people can type into, not a picture of one. How that works.

Notes for cURL extension

Plain ext-curl, no Composer needed. The details that bite: CURLOPT_RETURNTRANSFER must be set or the bytes are echoed to stdout instead of returned; the HTTP status has to be read explicitly with curl_getinfo() because cURL happily "succeeds" on a 401; and response headers need a CURLOPT_HEADERFUNCTION callback if you want to check things like X-Form-Fields. file_put_contents is binary-safe in PHP — strings are byte arrays — so no "b" flag dance is needed.

Response headers worth reading

Header	Meaning
`X-Cache`	HIT = served from the 24h cache, free.
`X-RateLimit-Remaining`	Requests left in the current second.

Full parameter reference: the docs. Hard numbers on caps and timeouts: limits.

Convert a URL to PDF in PHP with cURL extension

Notes for cURL extension

Response headers worth reading

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