A supplier sends you the signed contract as a PDF. Page six carries a signature in blue ink, scanned from paper. Eighteen months later a dispute starts. The supplier's new management says nobody there signed that. What are you actually holding?
A picture of a signature. It shows that an image of a signature exists. It does not show who held the pen. It does not show which paper, or which day. An image can be lifted from one document and dropped onto another in a minute.
What a scan shows, and what it does not
A scan answers one question only: does an image of a signature exist?
A scan of a wet-ink signature is a file of pixels. Nothing inside the image ties it to the text above it or to a date.
What Swiss contract law says about signatures
Swiss law starts from a hand on paper, and names one electronic route that counts the same.
Most contracts in Switzerland need no particular form (Article 11 paragraph 1 of the Code of Obligations). Some contracts must be in writing by law. For those, Article 13 paragraph 1 says the contract must be signed by all persons it imposes obligations on. Article 16 paragraph 2 applies the same rules when the parties chose written form themselves.
Article 14 then says what a signature is. Paragraph 1: "Signatures must be appended by hand by the parties to the contract." Paragraph 2: "A signature reproduced by mechanical means is recognised as sufficient only where such reproduction is customarily permitted, and in particular in the case of signatures on large numbers of issued securities." Paragraph 2bis: "An authenticated electronic signature combined with an authenticated time stamp within the meaning of the Federal Act of 18 March 2016 on Electronic Signatures is deemed equivalent to a handwritten signature, subject to any statutory or contractual provision to the contrary."
A copied signature counts only in narrow, customary cases. The one electronic route the Code names runs through the Federal Act on Electronic Signatures (ZertES). A scan of ink is none of these. Does a given contract need written form at all? That is a legal question about that contract, answered by Articles 11, 13 and 16. (Fedlex text re-checked 15 October 2026.)
When the scan is disputed
If the other side disputes the scan with good grounds, you must prove it is genuine.
The Civil Procedure Code counts electronic files as physical records. Article 177 defines them as "documents that are suitable to prove legally significant facts, such as papers, drawings, plans, photos, films, audio recordings, electronic files and the like as well as private expert opinions obtained by the parties".
Article 178: "The party invoking a physical record must prove its authenticity if this is disputed by the opposing party; the opposing party must give adequate grounds for disputing authenticity." Article 180 paragraph 1 adds: "A copy of the physical record may be produced in place of the original. The court or a party may request that the original or an officially certified copy be produced if there is justified doubt as to the authenticity of the physical record."
A scan is a copy by definition. If the paper with the ink is gone, there is no original to produce. The pixels cannot say who signed.
What a seal over the scan adds
A seal fixes the file and the date, so any later change to the PDF is detectable.
When you seal the PDF on Swiss Trust Layer, a cryptographic fingerprint of the file is computed. Only that fingerprint goes to Swisscom Trust Services, the qualified trust service provider. The file itself is never sent. Swisscom signs the fingerprint with a key that never leaves its hardware. The signature carries a timestamp under RFC 3161 and is embedded in the PDF. The original file is not altered. The folder gets a certificate of proof. It lists the file, its fingerprint and the sealing time in UTC.
Any change to the file now produces a different fingerprint, so it is detectable. Under Article 41(2) of the eIDAS Regulation, a qualified electronic time stamp carries a legal presumption. The date and time it shows are presumed accurate. The data bound to it is presumed intact. Anyone can check this on the public validator at swisstrustlayer.com/validate, with no account. It reports who signed, when, with which certificate, and whether the content was modified after signing. The document itself is not stored. Was page six swapped, or a clause edited later? The seal answers that.
The limit, stated plainly
A seal proves the scan existed unchanged on the sealing date, and nothing about the handwriting.
It does not prove that the handwriting is genuine. It does not prove who held the pen. It does not turn a picture of a signature into a signature under Article 14. A timestamp cannot be added backwards. The seal is strong on integrity and date, and silent on identity. We drew that line in a timestamp proves existence, not identity.
When the law asks for a real signature
If written form is required, use a qualified electronic signature, not a scan.
Article 14 paragraph 2bis names the alternative. It is an authenticated electronic signature combined with an authenticated time stamp under ZertES. In plain words: a qualified electronic signature with a qualified timestamp.
Swiss Trust Layer has a multi-signer flow for this. The owner of the folder adds the signers by name, email and phone. A signature field is placed on the PDF for each one. The owner signs first. Then each co-signer signs with their own qualified electronic signature. The public validator recognises eIDAS and ZertES qualified signatures. It reports who signed, when and with which certificate. Each signer's own qualified certificate answers the identity question the scan left open. Whether a signature meets the form rule for a given contract stays a legal question.
One step this week
Find one contract that rests on a scanned signature and still matters.
If it needs written form, a scan will not settle it. The route the Code names is a qualified electronic signature. If a scan is all there is, seal it now. From today the integrity and date question is closed. Keep the paper original if you still have it. Article 180 may ask for it. More on how it works and in ten questions a lawyer will ask about your PDF.
Seal your first document on Swiss Trust Layer and know which question it answers.
