Today, most smartphone and tablet vendors do a good job of limiting usage to certified and approved applications. Some would argue they do too good of a job restricting access. Other vendors maintain a very open policy for creating applications, with no formal process for certifying apps. That said, certain organizations or industries may need to restrict the type of application allowed on a corporate-approved device.
If you want to be proactive about it, set up your own enterprise application storefront. This allows you to present a list of approved applications and ease their delivery to mobile devices. Plus, your users will know where to go for these applications and for updates. Some MDM-solution providers can even help you deliver documents such as PDFs to devices.