How to sign a contract over WhatsApp without losing validity
Sending a contract over WhatsApp is practical and lawful — as long as the channel is how you deliver it, not how you prove it. The difference is one detail.
In Brazil, WhatsApp is where business happens. Denying that costs sales. The question is not whether you can use it, but how to use it without turning your evidence into a screenshot of a chat.
The common mistake: closing the deal in a screenshot
Dropping the PDF in a group chat and treating an "ok, agreed" as a signature works right up until it does not. A screenshot proves little: it does not show whether the file was changed afterwards, it does not identify the signer with any certainty, and it depends on the conversation still existing on somebody's phone.
The right way: WhatsApp as delivery
The correct approach is to use WhatsApp to deliver the link and, if you like, to deliver the confirmation code. The document itself stays on a platform that records everything:
- The signer gets a unique link that only they hold.
- They open the document on their phone and read it — the opening is recorded.
- They receive a single-use code, by WhatsApp or e-mail, whichever they chose.
- They confirm the code and sign. IP, carrier, city and official time go into the trail.
- The sealed PDF comes back to them through the same channel.
None of this requires the signer to install an app or create an account. From their side, it is opening a link and typing six digits.
Why a separate channel for the code matters
The code is what turns "somebody opened the link" into "this person signed". It goes to an address or a number that belongs to the signer and was agreed beforehand. If the code reached their phone and came back typed correctly, there is one more link between the person and the act.
That is why the choice of channel should be the signer's, not yours. Someone who does not use e-mail daily will be slow — or will never see it. Someone who prefers e-mail does not want their number in your system.
What to keep afterwards
Keep the sealed PDF, not the screenshot. The final file already carries the signature report, the timestamps, the origin of each signature and a public verification code. If you switch systems tomorrow, the document still proves itself.
About approved templates
Automated business messages on WhatsApp go through templates approved by Meta. That is a good thing: it means the message arrives as official communication from a verified company, not as a stray link from an unknown number — which on its own raises the odds that the person opens it.