SharePoint by default turns on a security feature that prevents people from opening PDF files directly in the browser. Need to open and read a PDF file from SharePoint website you need to download and save it to your local computer first, which is annoying. While I understand the necessity of this feature turned on at a large scaled public SharePoint site I don’t see it makes too much sense on an internal Intranet.
So, at my work, I turned it off. And here is how:
1. Go to SharePoint Central Administration, either remotely or locally on SharePoint server.
2. Go to Manage Web Applications.
3. Select the row of the application that points to the site you want to make change, and click General Settings at the Ribbon bar.
4. Scroll the page a little to locate the section called Browser File Handling, and check the option Permissive.
5. Click OK to save the settings, and done.
The option Strict adds headers that force the browser to download certain types of files while the option Permissive doesn’t.
The limitation of changing the option to "Permissive" is that SharePoint then allows all types of documents be opened in the browser. There is no "out-of-box" option to allow this option for PDF files only. To find more how to get around with it, check out this post.