A common reported annoyance is the prompt to Open or Save PDF files from SharePoint Online in Office 365. The following aspects provide the requirements necessary to open PDF files directly in a browser:

1.  New and improved PDF support. A service update to Office 365 was rolled out in May 2012 to allow users to open PDF files from a SharePoint Online document library directly into Adobe Reader. See related Microsoft TechNet blog post: SharePoint Online: Service Update.
2. Latest Adobe version required. The latest versions of Adobe have added seamless PDF integration with Office 365. Download and install the latest Adobe Reader or upgrade your Adobe suites. Do not install the Google Toolbar or Chrome browser. The toolbar has known compatibility issues with SharePoint Online and Internet Explorer is the preferred browser for the best user experience.
3. Other workarounds not supported. There are various posts concerning enabling permissive mode or a site collection feature to open documents in client applications by default. Permissive mode is only available for on premise SharePoint installations and not recommended for security risks. Opening documents in client applications by default only works for certain file types, bypasses Office Web Apps, requires the latest versions of applications, and may still prompt to open or login based upon file version and Internet access security.

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Published by Kevin Fream

Many people don't understand their current situation and become frustrated in business and life, so I created the Delta Method and wrote the #1 Best-Seller "Change Your Game" - as featured at Harvard and NASDAQ as well as national TV news. Streamline your technology for competitive advantage using vetted IT support and take a divergent approach to personal growth. View all posts by Kevin Fream