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Re: Digital signatures in PDFs

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From: Duff Johnson
Date: Aug 2, 2013 10:05AM

> What are the best practices for setting up digital signatures in a PDF?
>
> Not talking about a graphic of someone's signature, but those verified
> electronic signatures you register with Adobe and other certifying
> companies.

I'm not sure what you mean by "best practice". Is a digital signature field, and the dialogs it spawns as/when needed, accessible? That's a question for each Reader developer (Adobe or otherwise), but in principle (and so far as I know, in practice with Adobe's Reader, anyhow) the answer is "yes".

If there's contrary information out there, I'd be very interested to hear specifics (offline, preferably).

> When a PDF is created, we have the ability to add a Digital Signature field
> (technically it's a form field, even if there aren't any other form fields
> in the document).

Yes - it's a "digital signature field" - a specific type of form field, and it shows up to AT just like any other form field. It has lots of additional functionality, but that stuff is represented within dialogs managed by the application and isn't inherent to the PDF.

> Is there anything else that needs to be done to make it accessible?

Adobe's Reader can report on the field's name (label) and value (signature status and metadata).. the latest (Acrobat/ Reader XI) dialogs are (so far as I know) operable - there's no (good) reason why they shouldn't be. I will admit I've not looked at this in some time.

Now - obviously, a user could do something tricky, like include inaccessible information in an image or avatar they use to help "identify" themselves in the signed digital signature field, but that's kind of normative whenever images are concerned.

I guess my point is: there's no reason in principle why digital signatures in PDF shouldn't be completely accessibleÂ… and in fact, every reason why PDF digital signatures *should* be a highly desirable implementation from an accessibility point of view. Sadly, this feature remains lamentably under-used in PDF irrespective of accessibility considerations, but that's for reasons I won't get into here.

> And how difficult is it for AT users to sign with a digital signature?

Once again, this isn't really a PDF question but a matter of UI design in presenting (any) digital signature field information to the user, regardless of the underlying file.

There are several moving parts. Before being able to digitally sign in the first place it's necessary to create a certificate, for example. All users have to figure out / walk through and (pretend to) understand this stuff; that's not an accessibility issue per se.

Are all your favorite vendor's application dialogs good-to-go from a keyboard user, contrast, text size, other other standpoint? The answer vary from implementation to implementation, but it "should work". If it doesn't, say something.

Duff.