One of my colleague was working with file downloading functionality in SP2010. And she found weird behavior on different SharePoint Servers. I found it is a matter of configuration only from Central Admin site.
This problem has arisen quite a bit since the release of SharePoint 2010. On the MSDN forums, there are many questions that seem new, but they always end up coming down to one setting.
In SharePoint 2010, there is a new setting at the web application level called Browser File Handling (as below figure). You get to this setting with these steps:
1. Central Admin > Application Management > Manage Web Applications
2. Single-click the row of your web application
3. Click General Settings in the ribbon
4. Scroll down to Browser File Handling and select Permissive
By default, this is set to Strict when creating a web application. However, this causes issues in many ways related to opening certain files from SharePoint. The most obvious example is with PDFs. When set to Strict, a PDF can only be Saved (downloaded), but in Permissive mode, the PDF can be opened directly.
Hope this will help someone…