Signing PDFs: A Drawn Signature Is Not a Digital Signature

One word covers two completely different things. One puts a picture of your signature on a page; the other proves mathematically that the document has not changed. The gap between them is technical, not just legal.

Two separate operations

A drawn signature behaves like its paper equivalent: the other party sees it and usually accepts it, but it can be copied and it says nothing at all about whether the document was altered afterwards.

When a drawn signature is enough

Most day-to-day workflows expect exactly this and are satisfied by it: delivery forms, onboarding paperwork, draft leases, school permission slips, internal approvals. When someone says "sign and send it back", this is nearly always what they mean.

What makes this kind of signature credible is not technology but context: which email address it came from, when, and as part of which thread. That is what actually gets weighed in a dispute.

When you need a digital signature

A digital signature takes a digest (hash) of the document and encrypts it with your private key. The result is embedded in the file. Change a single character and the digest no longer matches, so any reader shows the signature as invalid.

That means a digital signature proves two things at once: that the document has not changed since signing, and that the signature belongs to a specific certificate. This is what public authorities, e-invoicing systems and most tender processes require.

Order matters: sign last

Any operation performed on a digitally signed PDF invalidates the signature. That is not a limitation, that is the signature working as designed. The practical consequence:

1. Finish the document.
2. Merge if you need to.
3. Compress if you need to.
4. Flatten any forms.
5. Sign last.

Compress after signing and you have personally broken a technically valid signature — and the other side sees it as "this document was modified".

Practical warnings

• Do not send the signature page alone: A single page proves nothing about which document it belongs to. Sign the whole file.
• Do not paste a cropped scan: A signature sitting inside a white box looks bad and invites suspicion.
• Do not leave the date blank: An empty date field leaves the document open to being completed later.
• Flatten it: A signature left as an editable field can be deleted by accident on the other side.

In short

If nobody is asking for a wet signature or a qualified electronic signature, a drawn signature is almost certainly enough and takes seconds. If the document is going to a public authority, a certificate-based digital signature is mandatory and no drawn image can substitute for it.

Frequently asked questions

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