Internet Explorer 7 and 8 may fail to open PDF files when the file is opened using a direct link.
For example, this may happen when the link to PDF file is shared via email. This problem occurs when PDF files are stored as media items in the Sitecore CMS and the MediaResponse.Cacheability setting is set to NoCache.
This behaviour is caused by a bug in the Internet Explorer browser.
Use one of the following solutions to fix the issue: