点这个链接查看详细的解决办法

http://helpx.adobe.com/acrobat/using/display-pdf-browser-acrobat-xi.html

When you click a PDF link on a web page, it can open either within the web browser or directly in Acrobat or Reader. Each browser has its own settings to control how PDFs open from a web page. Acrobat XI and Reader XI do not include a preference setting to open web-based PDFs. To change the display behavior, follow the instructions below for your browser, or see the browser documentation on how to control plug-ins or add-ons.