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That all really depends on what you are trying to do. If you simply need to open and view PDF files, then Adobe Reader will suffice and is easily downloaded from www.adobe.com. If you need editing capability, all versions of Adobe Acrobat (8 - 10) allow you to export to MS Word. First try opening the document in adobe reader, (it will help determine if the document is corrupted or some other incompatibility is keeping it from opening) and second, try reinstalling your version of Adobe Pro 8.3.1, or Update/Upgrade to the latest version.
See this link for a workaround: Free Trial of the latest version of the software. No cost, and seems to be fully functional for 30 days; however, it will uninstall your current version if you do not un-check the "remove current versions" checkbox during installation. To purchase, this one actually will allow you to buy in at roughly 15 USD a month, rather than $500 + dollars, see the link for more info! :)
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