Let me say up front that I detest handling PDFs on mobile devices. Sure, they're easy to muck around with on the desktop and yes, it's easy to view on your mobile devices such as the iPad, but when it comes to getting a signature or exporting a file to a PDF, the desktop reigns supreme.
iPhone and iPad apps tagged "digital signature."
Enhanced eFax App Does More Than Mobile Faxing
Cloud-based service provider eFax has unveiled an enhanced iPhone app with a new digitized signature feature. The new app enables mobile professional subscribers to easily sign, approve or initial important business documents such as contracts or invoices directly from their smartphone.