Prevent caching of URL redirect to file
I'm guessing you mean the Redirect module, not the Global Redirect module.

One thing to clarify: Are you trying to change the actual destination of the redirect (by initially having example.com/newsletter redirect to sites/files/upload/newsletter.pdf one day, then the next day having it redirect to sites/files/upload/newsletter-2.pdf)?  Or (as I think you're saying) are you actually overwriting newsletter.pdf on the server so that it's a different file?

I'll assume you're doing the latter.  If so, then the type of redirect doesn't matter.  You're facing caching on the browser side and you need to change your mod_expires settings.  Assuming you're allowing htaccess files to influence your apache configuration, you can put the following in the mod_expires section of your .htaccess file in the root of your site:

ExpiresByType application/pdf A86400


That would make browsers cache PDF files for a day (86,400 seconds).  An alternative, equivalent syntax is:

ExpiresByType application/pdf "access plus 1 day"


You can adjust that parameter however you like.  See documentation here.