The PDF case is no problem with the builtin PDF support in Chrome and Firefox. Or if you like the Adobe stuff, just disable the plugin and you'll automatically get the download and then a prompt to launch Acrobat Reader.
This is similar to forcing links to open in new windows - assuming the user is stupid in a way that doesn't even let the user to revert to the normal web behaviour (no browser function to "open in same window" vs no browser function to "open in browser")
This is similar to forcing links to open in new windows - assuming the user is stupid in a way that doesn't even let the user to revert to the normal web behaviour (no browser function to "open in same window" vs no browser function to "open in browser")