Changing Which Program Opens What Kind of File

Don’t you just hate it when you double-click a file and it opens up in the wrong program? For instance, a .PDF opening up in Acrobat instead of Preview, .mp3 in iTunes instead of Cog, or a webpage in Safari instead of FireFox (or the other way around). Most power users know instantly what to do to change this, yet not everyone is a power user. Fortunately, this is a really easy thing to fix.

Default Applications:

Default applications are the programs that open up certain file types. Preview will open up .PDFs by default unless you install Acrobat – which likes to take over as the default application. These are set automatically by the OS for common filetypes that it can support, like pictures, web pages and movies. For custom filetypes that work only with specialized software, their default application is set when you install the program.

How does the OS tell these files apart?

Contrary to what you may think, the OS doesn’t know a JPEG picture from a MP3 music file – or any other filetype. It needs to be told what kind of file it’s opening and what application to use. OS X does this by using File Extensions.

A File Extension is basically the three or four letter code after the filename, separated by a dot. For example the following are common file extensions:

– Article.pdf
– Music.mp3
– Image.jpg
– Webpage.html

Before OS X, the Mac OS didn’t use file extensions (the 3 letter code after the dot in a filename – Picture.jpg for example). OS 9 are earlier knew which application to use through hidden information within the filesystem. Personally, I like the file extensions better because you can easily change them if you need.

To make things simple, OS X allows you to hide these File Extensions. Trust me, all files have them unless they are given an icon that looks like a blank white square. If you are hiding them, you can show them by:

– Clicking “Finder” from the MenuBar and choosing “Preferences”.

– Click the “Advanced” tab at the top.

– Check the checkbox next to “Show all file extensions”.

Changing the Default Application:

Now that you know how OS X figures out what kind of file it’s opening, let’s learn how to change the application OS X uses to open a particular file type. Pick a file of your own but make sure it’s not an Application such as Safari or Microsoft Word. For my example, I will choose a .mp3 file and change the default application from iTunes to Quicktime Player.

– Single click the file to highlight it.

– Click “File” from the MenuBar and Choose “Get Info”.

Note: You may also Control-Click and choose “Get Info” or use the Command + I keyboard shortcut.

– A large rectangular information box will open up.

– Read down to where it says “Open with:”.

– Click on the triangle to expand the box if it’s closed.

Changing the default application

– You will see the default application. Let’s change it.

– Click on the Application name.

– A box will open up highlighting some common choices.

– If the application you want isn’t listed, click “Other…”.

Changing the default application

– A dialogue box will open up showing the Applications folder.

Changing the default application

– Scroll down and pick the Application you want to use.

Note: If the Application you want to use is grayed out and you can’t select it, click on the box next to “Enable:” where it says “Recommended Applications”. Choose “All Applications”.

– Finally, click “Add” to select the Application.

– If you want to use this Application for every file of that file type, click the “Change All..” button.

– Enter the Administrator password if prompted.

This a simple yet powerful trick. However, if this seems to be over your head in difficulty, Rubicode created the excellent freeware RCDefaultApp to help you do this, and a little more, in an easy to understand way.

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