Generally, the browser is decoupled from the operating system's file system to enforce security, so that mischievous webmasters don't access people's hard drives.
If you want to offer users a PDF invoice by email, you might want to use XSL-FO, and if you do then you will want to install an xsl parser on your server to do it. FOP is an open source (i.e. free-to-use) parser, but the XSL-FO learning curve might cost you. Other solutions exist as well, so you might want to research options and select the one that suits you best.