You mean on Windows Phone? If yeah, I think you cannot. The Internet Explorer browser is programmed to prompt you to choose what to do with a file that has a .PDF extension whenever you click download. You can always save and find it in your DOWNLOAD folder on Phone or SD Card or if you choose to open, Windows Phone detects a PDF App (Adobe, Tucan, Reader etc) and opens it with it. Mind you, if you choose to open, you cannot access the downloaded file except through the app you used to open it.