How to add .pdf support to the WordPress media manager

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By default, the built-in WordPress media manager allows you to filter media by three types: images, audio and video. But if you work a lot with .pdf files, you may need to add an option to filter .pdf files from the media manager. Here is a simple code snippet to do it.
Paste this code into your functions.php file. Save the file, and you’re done.

Note that this code snippet can be used for other file types as well as .swf, .avi, .mov, etc.