Most browsers will open a pdf in the browser window by default, unless the user has set the browser to do otherwise in the preferences. The pdf viewer will automatically fill the window with the document. The catch is if the clients don't have acrobat installed on their machine. So what you'll want to do is send them a link to a page which has some javascript that determines whether or not they have acrobat installed, if not, they get sent to the acrobat download page. Otherwise they get sent to the pdf.