Newer versions of Adobe Reader (X) have a SharePoint Integration feature set.  Part of this integration involves a check in/out prompt when clicking on a PDF file located in a SharePoint Library.

Even if the library itself does not have "check out" enabled, Adobe will prompt the user to either "Open" the file or "Check Out and Open" the file.  

Adobe - SharePoint 2010 Integration

The rub is that even when this feature is NOT enabled in the library itself, if a user clicks "Check out and Open", the file will be checked out in the SharePoint Library!!!  Adobe Reader DOES have an option to Check In, buried in the File menu.  But who is ever going to see or do that?  It's more of an annoyance that anything, at least for my environment, since PDF files typically cannot be edited anyways…

Currently, there is no direct fix for this.  The only option is to disable the Adobe Sharepoint Integration entirely (in the client Registry), which is not very attractive for a number of reasons.


Add this to the list of even more reasons not to like Adobe Reader.  Read more here: