Your best option is to upload the contract and any other pdf, music, video file, etc using FTP program. Store them directly on your website.
THEN link to the file in CSB.
For this item the easiest way to do what you want:
1) upload the pdf file to your website with FTP or your control panel at your host'
2) Open CSB to the page where you want the link
3) Use a URL style link. Link to the file and set your TARGET to blank.
Look at this page.