where is the PDF placed? You have it inserted in content tree as a file, you can simply go to Properies ~ URLs and click Add new alias. Then you type the alias to Path or pattern. Take care, the page will not have pdf extension. When you type /testpdf, the address could be http://localhost/testpdf.aspx
If you do not have your PDF in content tree, simply create new page and go to Properities ~ Navigation and enter URL of the pdf to Menu actions / URL redirection. You can set alias to this page then if needed.