With Siri and App intents can a document signing app create an experience like - Sign documents with your voice?

Yes — a document signing app could potentially create a voice experience like “Sign documents with your voice” using Siri + App Intents, as long as the app exposes the right action as an App Intent.

From WWDC, Apple explains that:

App Intents let Siri and the system invoke your app’s actions.
Siri can then execute those actions directly, without you handling natural language yourself.
App Schemas make those actions more understandable to Siri in supported domains.

So for a document signing app, if you define an intent like:

SignDocumentIntent
with parameters such as the document and signer options,

then a user could plausibly say something like:

“Sign this document”
or “Sign the latest contract”

and Siri could run that action if your app supports it.

That said, whether the exact phrase “Sign documents with your voice” works depends on how your app’s intents are designed and what capabilities are exposed. WWDC doesn’t say that this specific document-signing use case is built in by default, only that apps can expose actions for Siri to perform.

So the short answer is: yes, in principle — if your app models signing as an App Intent and makes it available to Siri.