give :disposition => ‘inline’ in your controllers
There are several quirks with sending inline to most browsers (for example if I remember right Firefox is still plagued by not using the name you set for inline) and IE has several bugs that used to exist but I don't know if that's the case. I would suggest you send it as an attachment and let the client decide what they want to do, actually IMO you should always send it as an attachment no matter what because it should be up to the client what they want to do, that's why the "open with" exists.
Adobe can catch them even if they are attached on Windows, on Linux you won't want to view it inline anyways (at least I never do I prefer to view it in my client rather than the browser -- or to send it straight to Google Docs for viewing later.)
send_data(file, type: "application/pdf", disposition: "attachment; filename=file.pdf")