is not to right click and 'save target as'.
The link to the PDF will automatically download the file to the visitor's machine on a left click - provided he/she has the Acrobat reader installed. The normal procedure would then be for the person to save the file on their drive in the normal way - if he/she wanted to.
It doesn't matter what you do, the file can only be opened in the PDF reader anyway, and I can see no point in trying to make it more complex than that, and you certainly don't need to involve Java script. Just put the PDF file on the server (it's a good idea to keep it in a separate PDF directory) and then hyperlink to it in your HTML page in the normal way. The visitor's browser will do the rest.
It helps to provide a separate link to the Adobe site as well - so that people who may not have the Acrobat reader can download it before attempting to retrieve your file. Use a text link:
"You will need to have Adobe Acrobat reader installed on your machine before you can view this file. If you don't have the reader you can download the latest version HERE"
Make "HERE" a hyperlink to Adobe.com