Sometimes when you click on a link to a PDF, it comes up in the browser. Other times, the browser downloads the file. Everyone must wonder why, but few have wondered enough to find out. Here’s a quick explanation.
It has nothing to do with the PDF version, the content of the file, or the link. It’s the HTTP headers that make the difference. Specifically, a header called “Content-Disposition” is the determining factor. If it’s absent, the file will open in the browser. If it’s present, the value it specifies determines how you get the file.