It is a known issue on Windows 7 X64. Microsoft Windows 7 Starter, Home Premium, Professional and Ultimate / Enterprise 64-bit is supported after the 9.2 update has been applied. It is required to download a hotfix, which is recommended from Microsoft. Though it is based on Vista 64, but it works on 7 also.
Or if u get this problemsome, then try out this…..
IE8 > TOOLS >COMPATIBILITY VIEW SETTINGS and add the website that hosted the PDF file. For more info to resetting IE8, please visit here.
And the last word, if all the above will not work, u may go for FoxIt Reader, free and tested. For download please link here.