E-signatures for vendor and supplier agreements

What vendor and supplier paperwork needs signing

• Master supply or services agreements: the terms behind every order, such as prices, delivery, quality standards, payment terms and liability.
• Purchase agreements for a single large purchase, such as a machine or a fit-out.
• Amendments and renewals: a new price list, a longer term or a new delivery site.
• NDAs before you share drawings or forecasts with a new supplier. See how to sign an NDA you can prove.
• Supplier acknowledgments, such as a code of conduct the supplier confirms it has read.

With Attest, each one is a PDF of up to 8 MB that you upload. One document can have up to 20 signers, on your side and the supplier's.

The question in a supplier dispute: which version?

Supplier disputes turn on which price list applied, which delivery terms were in the version signed, and whether a later change was ever approved. Attest's evidence answers exactly that:

• Which price list. Each signer's passkey signs a statement that names the document's fingerprint (a SHA-256 hash, a short code calculated from the file's contents) and everything that signer entered. If the price list attached to the agreement changes by one figure, so does the fingerprint.
• Which approver, on each side. Your approver and the supplier's signatory each sign with a passkey, a cryptographic key only the signer controls, unlocked with Face ID, Touch ID, Windows Hello or the device PIN, and registered to their own email address.
• Which date. Each signer's signing time is in the statement their passkey signs, and the completed agreement is anchored on Horizen, a public blockchain, so its block time dates the version both sides signed.
• No silent edits. Change one byte of the document, of any signer's entries or of the signed pages, and verification fails.

Both companies download the same sealed PDF, which carries its own evidence, the original document and an open-source verifier inside it. Your finance team or an auditor can check it for free at attest.datahubz.com/verify, with no account, and the verifier inside the PDF works in any browser even if Attest is gone.

Your paper or theirs

When you send your own agreement, list everyone who signs. A common order is the supplier first and your approver last, so your side countersigns the version the supplier has already signed. If you sign too, check Add me as a signer (sign in-app, no email); then pick In order under Signing order with the supplier listed first, and next to I sign choose Last. In order mode, Attest emails only the signer whose turn it is, and emails the next one as soon as they sign. You are never emailed for your own turn: once the supplier has signed, the agreement moves to Action needed in your dashboard, with a Sign button on its row.

When the supplier sends its own contract as a PDF, click Sign a document yourself, place your signature, sign with your passkey and send back the signed copy, which the supplier can check for free with the verifier attached inside. This uses one of your documents, because it creates a document in your account; if the supplier sends it to you through Attest instead, signing it is free.

Negotiate first, sign once. Redline in your usual editor and send only the final PDF. A later change goes out as its own amendment that names the agreement it changes, with its own fingerprint, certificate and anchor.

Keep supplier prices private, from Attest too

A supply agreement carries the numbers both companies guard most: unit prices, volume discounts, rebates and penalties. Most e-signature services describe their protection as encryption in transit and at rest, and describe no end-to-end mechanism, so their systems can decrypt the documents they store. We compared 21 e-signature services in October 2026, Attest and 20 others, and Attest was the only one that end-to-end encrypts every document, for every signer, by default.

End-to-end encryption means the agreement is encrypted in your browser before upload and decrypted only in the browsers of its parties, so the supplier's prices and yours stay between the two companies. Attest stores it only as ciphertext it can't read.

Attest does see the information around a document, such as its title, file name, your note and the signers' emails and names. So use a neutral title, such as "Supply agreement 2027", and choose Private under Verification: only the parties then see the agreement's certificate, which by default shows anyone with its link the title and each signer's name and signing time, among other details, though never the document.

Prove a supplier contract exists, without sending it

A customer may ask whether you have a supply agreement in place for a critical part, without needing the prices. On a completed agreement you signed, Share proof creates a zero-knowledge proof: a proof that a statement is true which reveals nothing beyond the statement. It can state that you and a named co-signer, such as the supplier's signatory, signed an agreement, and the date it was completed.

The recipient sees both email addresses, the completion date, and that the proof is valid and where its record is anchored; the document and its terms, its title and any other signer are never shown. Each proof is submitted to zkVerify for independent verification, and anyone can check it for free. Proofs are made by signers, so add yourself as a signer when you send. More in proving a partnership or contract is in place.

Before the contract, on Pro: sealed bids and supplier approval

Attest Pro, $49 a month, adds Sealed submissions: bids, proposals or applications that no one can open before the deadline, not you and not Attest. Each bid is encrypted in the bidder's browser and time-locked until the deadline, which you set between 5 minutes and a year ahead, and the call's terms are anchored when you create it.

Pro also issues Proof Cards, credentials your organization signs, including supplier approval: a supplier that passes your checks gets a card it can share as a link or QR code, which you can suspend or revoke at any time, and whoever checks it sees its status live. Sealed submissions and Proof Cards are on Pro, not on the Signing plan.

How to send a supplier agreement

1. Open Documents in the menu (it reads Agreements on accounts that use every Attest tool) and click New agreement.
2. Give it a neutral Title, click Attach the document to be signed and choose the final PDF.
3. Under Signers, type the supplier signatory's email address, and click + Add signer for anyone else who signs, such as your approver.
4. If you sign too, check Add me as a signer (sign in-app, no email). Pick In order under Signing order with the supplier listed first, and next to I sign choose Last.
5. Under Verification, choose Private.
6. If the offer lapses on a date, set Expires (optional). Keep Reminders at every 3 days or choose another interval.
7. Click Next: place the fields, place a signature field for each signer, plus a date or full name field where the agreement asks for one, and click Create and send.
8. If a signer is new to Attest, Attest emails you once they have set up their key. Click Unlock it for … in that email (or open the agreement in Attest), confirm, and approve with your passkey: your browser releases it to them, never Attest.
9. When the supplier has signed, the agreement moves to Action needed (you get no email for your own turn). Click Sign on its row and approve with your passkey. When everyone has signed, click View the signed copy, then Download signed copy.

What it costs

Your first 2 documents are free, in total. After that, the Signing plan is $5 a month for 20 documents sent for signature, and you can cancel any time. Suppliers, and everyone else who signs, never pay, on any plan. Pro, at $49 a month, adds sealed submissions, Proof Cards and Attest's other tools, with 10,000 records a month; each document you send counts as one record.