Endpoint reference

`POST /api/set-metadata`

Write the Info fields of a PDF: title, author, subject, keywords and creator. Send any of them. Returns the updated PDF as application/pdf.

Request

Method: POST. URL: https://pdfops.dev/api/set-metadata. Body: multipart/form-data.

Field	Type	Required	Description
`pdf`	File (PDF binary)	Yes	Exactly one PDF, up to 4 MB and 2,000 pages. The whole request must stay under 4.5 MB, Vercel's platform request limit.
`title`	String	At least one of the five	Up to 1,000 characters.
`author`	String	At least one of the five	Up to 1,000 characters.
`subject`	String	At least one of the five	Up to 1,000 characters.
`keywords`	String	At least one of the five	Comma list. Items are trimmed and empty ones dropped. Up to 1,000 characters.
`creator`	String	At least one of the five	Up to 1,000 characters.
`password`	String	No	Opens a PDF that needs a user password. Not needed for owner-locked files with an empty user password.

The optional X-API-Key header works as on /api/merge: no header is anonymous, 100 requests per IP per month; a valid key uses your tier's quota; an invalid or revoked key returns 401 invalid_api_key. A successful (2xx) call counts 1 request. Check consumption with GET /api/usage.

Response

On success: 200 OK, Content-Type: application/pdf, body is the updated PDF.

On any failure: 4xx or 500, Content-Type: application/json, body is { "error": "<code>", "details": "<explanation>" }.

Error codes

Error code	Status	Trigger
`invalid_multipart`	400	Request body could not be parsed as `multipart/form-data`.
`missing_pdf`	400	The request does not have exactly one `pdf` file field.
`pdf_too_large`	400	The `pdf` file is over 4 MB.
`invalid_pdf`	400	The PDF could not be parsed (corrupt, or not a PDF).
`encrypted_pdf`	400	The PDF needs a password we were not given. Owner-locked files with an empty user password (most government blanks) open on their own; for a real user password send it as the `password` form field.
`decompressed_too_large`	400	Object streams inside the PDF decompress to over 32 MB.
`too_many_pages`	400	The PDF has over 2,000 pages.
`no_fields`	400	None of `title`, `author`, `subject`, `keywords`, `creator` was sent.
`field_too_long`	400	A field is over 1,000 characters. `details` names it.
`save_failed`	500	PDF serialization failed. Retryable.
`request_too_large`	413	The whole request body is over 4.5 MB (Vercel's platform request limit). Rejected before anything is parsed.
`invalid_api_key`	401	An `X-API-Key` header was sent but the key is unknown or revoked. No fallback to the anonymous IP cap. Get a fresh key at /pricing.
`rate_limited` (anonymous)	429	No `X-API-Key` header and the per-IP limit (100/month) is exhausted. `Retry-After` gives seconds until next calendar month.
`rate_limited` (keyed)	429	Your key's tier quota (Free 250 / Indie 4,000 / Pro 25,000 per month) is exhausted. `Retry-After` gives seconds until next calendar month.

Example

curl -X POST https://pdfops.dev/api/set-metadata \
  -F "pdf=@report.pdf" \
  -F "title=Q3 report" \
  -F "author=Finance team" \
  -F "keywords=quarterly, finance" \
  -o report-tagged.pdf \
  -H "X-API-Key: pdfops_live_..."  # optional, raises your quota to your tier

Keyless calls work: 100 requests per IP per month with no key.

Using this for real? A free API key raises the keyless 100 calls per IP to 250 requests a month, with no card.

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Code examples

Have an API key? Add an X-API-Key header to any request. It is optional, and it raises your quota from 100/IP/month to your tier's.

JavaScript (Node.js 22+) — built-in fetch + FormData

import { readFile, writeFile } from 'node:fs/promises';

const fd = new FormData();
fd.append('pdf', new Blob([await readFile('report.pdf')], { type: 'application/pdf' }), 'report.pdf');
fd.append('title', 'Q3 report');
fd.append('author', 'Finance team');
fd.append('keywords', 'quarterly, finance');

const res = await fetch('https://pdfops.dev/api/set-metadata', {
  method: 'POST',
  headers: { 'X-API-Key': process.env.PDFOPS_API_KEY }, // optional
  body: fd,
});
if (!res.ok) {
  const err = await res.json();
  throw new Error(`PDFops set-metadata failed: ${err.error}: ${err.details}`);
}
await writeFile('report-tagged.pdf', Buffer.from(await res.arrayBuffer()));

Behavioral notes

Fields you do not send are left as they are. An empty string sets an empty value.
Unicode is fine here. Info strings are written as UTF-16.
Keywords are stored space-joined. That is how the Info dictionary models them.
The output is unencrypted. An owner-locked input is saved decrypted, as in /api/unlock.
The output is deterministic. The modification date and producer are pinned, and an existing creation date is kept.
Limits: 4 MB per PDF, 2,000 pages, 4.5 MB per request (Vercel's platform limit).

FAQ

Can I set the dates or the producer?

No. The modification date and producer are pinned by the service, and an existing creation date is kept.

How do I read the current values first?

Call /api/metadata.

Get a free API key. Keyless calls get 100 requests per IP per month; a free key raises that to 250, with no card. Enter your email and the key arrives in your inbox.

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