Now that most browsers have rudimentary PDF viewers built in or added on, our clients are frequently reporting errors when trying to view them - primarily in IE.
It would be great if there could be a Force Download checkbox in the media manager so that files can be made not to display in the browser on a case by case basis. This could also be handled with a global rule selectable in the UI to set certain file types as force download but that would give the user less flexibility.
Why not use a plugin? I've been researching these. The most popular ones involve adding markup like shortcodes or /download.php links to individual post content which would be a nightmare to manage on a large site. Others have aged out of official support or have support forums full of unresolved bugs and limitations. In a few cases, plugins and hacks to force PDF downloads have inadvertently created security vulnerabilities that allow critical php pages to be downloaded.