Extracting XMP Meta Information

Eventually embedded XMP meta information can be extracted and serialised into various formats:

import { PDFALab } from '@pdfa-lab/core';

extract().catch(err => {
	console.error(`Extracting XMP meta information failed: ${err}`);
	process.exit(1);
});

async function extract() {
	const url = 'https://github.com/gflohr/pdfa-lab/raw/refs/heads/main/assets/pdfs/factur-x-invoice.pdf';
	const response = await fetch(url);
	if (!response.ok) {
		throw new Error(`Failed to fetch ${url}: ${response.statusText}`);
	}

	const arrayBuffer = await response.arrayBuffer();
	const bytes = new Uint8Array(arrayBuffer);

	const lab = await PDFALab.from(bytes);
	const output = await lab.extractXmp(
		'text/turtle',
		'urn:xmp:doc',
		{ flags: 'o' },
	);

	console.log(output);
}

The method extractXmp() returns the extracted XMP meta information in various formats, or null, if no XMP meta information is found.

It takes three optional arguments. The first, determines the serialisation format (defaults to application/rdf+xml). The second argument specifies the base IRI (defaults to urn:xmp:doc). The third optional argument can pass options to the serialiser, currently only flags.

Output Format

pdfa-lib supports all output formats that rdflib supports:

Format	Aliases	Description
application/rdf+xml	xml, rdf+xml	The default output format, which is also the format embedded into a PDF document.
text/turtle	application/x-turtle
application/n-triples
application/ld+json
text/n3	application/n3
application/nquads	application/n-quads

Serialiser Flags

You can further control the output by passing flags. Flags can be combined (for example { flags: 'o k' }):

• s i – used by default for Turtle to suppress =, => notations
• d e i n p r s t u x – used for N-Triples/N-Quads to simplify output
• dr – used with JSON‑LD conversion (no default, no relative prefix)
• o – new: do not abbreviate to a prefixed name when the local part contains a dot. This keeps IRIs like http://example.org/ns/subject.example in <...> form instead of ns:subject.example.

Notes:

• For Turtle and JSON‑LD, user‑provided flags are merged with the defaults so your flags (like o) are honored.
• By contrast, passing p disables prefix abbreviations entirely (all terms are written as <...> IRIs).