Signing

typstgen does not sign PDFs. A signer appends the signature to a finished PDF as an incremental update, so the bytes typstgen wrote stay unchanged in front of it. That keeps the build reproducible and lets verify recognise the signed file.

For signing we recommend pyHanko (MIT, Python): PAdES baseline signatures up to B-LTA, RFC 3161 timestamps, PKCS#11 tokens and remote signing, and every write is an incremental update.

Do you need a signature?

This is background, not legal advice; as of October 2026, for Germany:

• Invoices, including ZUGFeRD: no. § 14 Abs. 3 UStG names a qualified electronic signature only as one way to ensure authenticity and integrity; an internal control procedure that matches the invoice with order, delivery and payment is enough (UStAE 14.4, BMF letter of 15 October 2025). If an invoice is sent with a qualified signature, the signature has to be kept with it.
• Archiving under the GoBD: no. A signature or timestamp is one possible measure for unalterability, not a requirement. The archive manifest and storage that cannot be overwritten are the usual route.
• Offers, order confirmations, most contracts: no form or text form (§ 126b BGB), so no signature is required. A signature only adds evidential weight.
• Contracts that need the written form: the electronic form needs a qualified electronic signature (§ 126a BGB). Some declarations, such as terminating employment (§ 623 BGB), cannot be made electronically at all.

A certificate you create yourself gives at most an advanced signature under eIDAS (Art. 26). Qualified signatures, seals and timestamps come only from a qualified trust service provider, for example as a signature card or a remote signing service; pyHanko works with both through PKCS#11.

Sign a PDF

Use pyHanko 0.35.2 or later: earlier versions rewrote the XMP metadata of PDF/A files with an extension schema, such as ZUGFeRD invoices, and broke their PDF/A conformance.

pip install pyhanko pyhanko-cli
typstgen compile rechnung.typ --pdf-standard a-3b --creation-timestamp 1737500000 \
  --zugferd rechnung.json --company company.json --manifest archive.json
pyhanko sign addsig --field Signature1 --use-pades \
  --timestamp-url http://timestamp.digicert.com \
  pemder --key key.pem --cert cert.pem rechnung.pdf rechnung-signiert.pdf

--use-pades writes a PAdES signature, --timestamp-url adds a timestamp from an RFC 3161 timestamp authority (TSA), so the signing time does not rest on the signer’s clock. With a PKCS#12 file use pkcs12 instead of pemder, with a token or signature card pkcs11.

Check the result

pyhanko sign validate --pretty-print --trust cert.pem rechnung-signiert.pdf
verapdf --flavour 3b rechnung-signiert.pdf
java -jar Mustang-CLI.jar --action validate --source rechnung-signiert.pdf

Run on 13 October 2026 with typstgen 0.5.0, pyHanko 0.37.0, veraPDF 1.30 and Mustang 2.26.0 on the example invoice of business-templates: the signature is valid and timestamped, and the PDF stays PDF/A-3b and a valid EN 16931 invoice.

For an independent check, the European Commission’s DSS demo validates PAdES signatures against the ETSI standards.

Verify the archive after signing

Replace the archived PDF with the signed one. verify finds the recorded build at the start of the file and reports what was appended:

$ typstgen verify archive.json
ok      rechnung.pdf
        note: signed after recording: the recorded PDF is unchanged, 1 revision(s) with a signature appended; check the signature with a PDF signature validator
1 of 1 documents verified

An appended revision can also change what the PDF shows, so verify only proves that the recorded build is intact. Whether the signature is valid and what the signed revision changes is the job of the signature validator. Revisions appended without a signature fail verify.

Timestamp authorities

TSA	URL	Notes
DigiCert	http://timestamp.digicert.com	free, widely used
Sectigo	http://timestamp.sectigo.com	free; at least 15 seconds between scripted requests
freetsa.org	https://freetsa.org/tsr	free, no service level; good for tests

None of these is a qualified timestamp under eIDAS. Qualified timestamps come from qualified trust service providers such as D-Trust, usually under contract; the EU trusted list lists them.

Why not a Rust signer?

In October 2026 we tested underskrift 0.1.4, the most complete PDF signing crate on crates.io, on the same invoice. Its signature was valid, but the trailer of its update had no /ID, which PDF/A forbids, so the invoice failed veraPDF and Mustang; timestamps set in its signing options were not applied. Of the other crates, pdf_signer is GPL-licensed and pdf_signing has not been updated since 2024. A signing feature in typstgen would add little: a self-made certificate only gives an advanced signature, and anything with legal weight needs a trust service provider, which pyHanko already supports.