Users cannot load an updated copy of a PDF on my website; they see a previous version of it.Help!

After saving and uploading a new version of a PDF file to my website, sometimes when browsing to that PDF in a web browser Adobe Acrobat will load the previous version (meaning the one that was there before I updated it). It's like Adobe Acrobat sees that the file the user is loading has the exact same name as one that was previously loaded on their system, so it just chooses to load that local one instead because it is obviously faster to load a local copy then a remote one. What I need is for Adobe Acrobat to download a new copy all the time. It appears the only way to force Adobe Acrobat to load the updated copy of the PDF is to rename the PDF filename when uploading it to my website. Unfortunately, this obviously necessitates all hyperlinks to that file be changed also, which is a pain. This problem appears no matter which browser the user uses, and clearing the browser's cache or private data or temporary internet files all have no effect. Even if the user right-clicks the file, saves the file to a local folder, browses to the file, then opens it in Adobe Acrobat, it will still load an old version. Please help!