Purchase Agreement attachments Permission

How do I make the Contract Purchase Agreement Attachments like "W-9" file for example available to regular users (non buyers) but we want to prevent users from updating the agreements. Currently we have the Purchasing Inquiry responsibility assigned to all users who are not Buyers to view only. They can only search agreements but cannot view the detail and attachments.  It's difficult to find the data security (if any) on the menu or function relating to agreements or agreement attachments. 

Please advise.

Thank you,

Susan