Sign a document without uploading it anywhere

A signature is a slightly odd thing to hand to a website. It is the mark you use to commit to contracts, and the usual way of adding one to a PDF involves uploading both the document and the signature to a service whose business model you have not examined. People do it because the alternative has been printing, signing, scanning and hoping the scan is legible.

Doing it locally removes that trade. The signature is generated here, the stamping happens here, and neither the image nor the document is transmitted. Which is the least you should expect from something whose whole purpose is applying your identity to an agreement.

It is worth understanding what this produces, because the vocabulary around signing is genuinely confusing. This makes a simple electronic signature: an image of your mark placed on a page. Under UK law that is admissible and is used for the great majority of commercial agreements without difficulty, since what matters is intent to be bound rather than the technology used.

What it is not is a digital signature in the cryptographic sense. It does not embed a certificate, does not prove the document is unchanged since signing, and does not carry an audit trail of who signed when. For most contracts that is fine and always has been. For anything requiring a qualified electronic signature, or where you may need to prove afterwards that the document was not altered, you need a proper signing platform and this is not one.

One practical note that catches people out: a signature saved as a plain PNG on a white background will sit on the page as a white rectangle over whatever it covers. Transparency is the difference between a signature and a sticker, which is why it is the default here.

The wider point, if signing is a regular part of the work rather than an occasional one, is that the bottleneck is rarely the signature itself. It is knowing which version was signed, by whom, and where it now lives, and that is a records problem rather than a PDF one.